Racial tensions in the United States are related to the role played by the slave system in the development of primitive accumulation in that country. Slavery existed throughout the Americas and the Caribbean (Brazil, Spanish colonies, the Caribbean islands) but in no other developed country has this system conditioned social relations and the obstacles to working class unity as much as in the US. At another level of development and importance, the case of South Africa has some similarities .
Capitalism in its origins, after the “discovery” of the Americas, was marked by slavery . And it was in the Americas in particular, not just in the US, that this system took root. To understand the history of the advent of capitalism, of the formation of the working class, including the present situation, it is necessary to address the problem of slavery.
The trauma of slavery, of the slave trade, has marked the history of the African continent of course, but above all, the history of the American continent in all aspects, in particular in the development of the working class. A large part of the American working class has its origins in slavery. We are not going to talk here about the role of the ruling classes (aristocracy and bourgeoisie) of the old European monarchical regimes in the abominable “triangular trade” between the main ports of the European powers, the African coasts and the Americas.
Slavery and primitive accumulation
As Marx writes: "The discovery of gold and silver in America [especially by the Spanish and Portuguese colonisers, Editors’ Note], the extirpation, enslavement and entombment in mines of the aboriginal population, the beginning of the conquest and looting of the East Indies, the turning of Africa into a warren for the commercial hunting of black-skins, signaled the rosy dawn of the era of capitalist production. These idyllic proceedings are the chief moments of primitive accumulation." (Capital, Volume I, Chapter 31, “Genesis of the Industrial Capitalist” )
The primitive capitalist accumulation under the old regimes, still marked by feudalism, was often carried out with slave labour. And Africa, to the misfortune of this continent, will continue to be, from the 17th, 18th and even much of the 19th century, an arena for “slave-hunting”. This type of exploitation will not be the same as that of capitalism, but its early days it served the process of primitive accumulation: “The sporadic application of cooperation on a large scale in ancient times, in the middle ages, and in modern colonies reposes on relations of dominion and servitude, principally on slavery. The capitalistic form [of cooperation], on the contrary, presupposes from first to last the free wage-labourer, who sells his labour power to capital. Historically, however, this form is developed in opposition to peasant agriculture and to the carrying on of independent handicrafts. From the standpoint of these, capitalistic cooperation does not manifest itself as a particular historical form of cooperation; but cooperation itself appears to be a historical form peculiar to, and specifically distinguishing, the capitalist process of production. (…) The simultaneous employment of a large number of wage-labourers in one and the same process forms the starting point of capitalist production.” (Capital, Volume 1, Chapter 9, “How Capital revolutionises the Mode of Production”, (A) “Cooperation”). Since capitalism began and developed in a non-capitalist environment, which at first was overwhelmingly dominant), it also developed in the midst of and thanks to other forms of exploitation and “cooperation”.
Feudalism brought under its control the old primitive communist communities that it “left alone” as long as they regularly paid tax in kind (agricultural, livestock or handicraft products) and in human beings (servants and soldiers). On the other hand, capitalism tends to transform all social relations into commercial and wage relations, and yet in the course towards them it is capable of using old forms of exploitation such as slavery, making them much more profitable through refined and systematic barbarism.
In the 19th century, slavery continued to exist on a large scale, as in the cotton-producing states in the US South: there were as many as 5 million slaves until well beyond the mid-century. They sold their production to the Northern states and, above all, to the first great capitalist country of the time, Great Britain. For decades, after American independence, the slave system remained vigorous  serving the process of accumulation in that immense country. But the confrontation between the capitalism of the Northern States and the slave States of the South became inevitable, in particular because of the expansionist dynamic towards the West, leading to the Civil War.
And, after the colonisation of Egypt, Great Britain began to stop buying the cotton of the South of the US. This, with the usual cynicism of the ruling classes, intensified the anti-slavery campaign waged by a good part of the British bourgeoisie .
And yet there was an exponential increase in the number of slaves over decades: " When, the first census of slaves was taken in the US in 1790, their number was 697,000; in 1861 it had nearly reached four millions", as Marx recalls in Capital (Capital, Volume I, Chapter 15 "Machinery and Modern Industry", Section 6 “The theory of compensation as regards the workpeople displaced by machinery”) And that took place in the US, the first country in the world “liberated” from the old regime, and together with France a “democratic” beacon for the rising bourgeoisies of other countries.
“Hence the negro labour in the Southern States of the American Union preserved something of a patriarchal character, so long as production was chiefly directed to immediate local consumption. But in proportion, as the export of cotton became of vital interest to these states, the over-working of the Negro and sometimes the using up of his life in 7 years of labour became a factor in a calculated and calculating system. It was no longer a question of obtaining from him a certain quantity of useful products. It was now a question of production of surplus-labour itself.” (Capital, Volume I, “The working day”, Section 2: “The greed for surplus labour. Manufacturer and boyard”). Despite these huge profits, it was still not a fully-fledged capitalist system.
The accompaniment of wage-earning exploitation by the system of racial segregation
The consequences of the "stain", that is to say the insult to human morality that slavery represented in the country that would end up being the most powerful on earth, did not disappear by magic after the Civil War. Slavery was gone, but not its consequences in the difficult struggle of the working class. As much as it was in the interest of the bourgeoisie to end slavery, we know very well that the ills of past class societies are concentrated in capitalism as if it were a melting pot of them all. The bloody Civil War  accelerated the spread of wage labour throughout the US, with black workers gradually being incorporated into "free" labour, but this "freedom to be exploited" was enveloped almost from the beginning by a system of racial segregation that added horrible suffering to this part of our class and created a dangerous division within the proletariat.
Racial separation laws remained in effect in virtually every state, backed by repeated sentences of the Supreme Court. The height of cynicism was attained by the Supreme Court, which only three years after the end of the Civil War (in 1868) ruled that “Negroes must live apart. The white man called them by their first name only and could abuse them for any reason. Blacks could vote, but only if they paid a special tax and the names of all Supreme Court presidents and judges were known by heart.” 
The legal system of segregation protected and encouraged a parallel, supposedly ”popular” system (thanks mainly to the fanaticism of the white petty bourgeoisie) of aggression, collective killings, and systematic lynchings. The petty bourgeoisie, especially in the Southern States, but not only there, unleashed their destructive fury with metronome regularity to terrorise the proletarians of slave origin. The racism of the American petty bourgeoisie reflects one of the ideological features of American capitalism: a culture imbued with a violent, biblically-inspired puritanism, one of the bases of which is the furious, visceral horror of any mixture of “races”. True, racism and the rejection of others is a widely shared mentality in all class societies, but in the case of the US it is a founding element of the country.
In Opelousas (Louisiana, 1868), New Orleans, and Memphis (1866) the white rabble reacted with lynchings to the attempts of the blacks to exercise the “new rights”. “In Thibodaux, Louisiana, 1887, more than 300 sugar cutters died during a strike for the right to stop living in the former slave quarters.” (https://www.lavanguardia.com/internacional/20200603/481582308546/violenc...)
The 20th century was even worse: "Up to 250 died in Wilmington, (1928 in North Carolina) including women and children when a white mob attacked one of their newspapers over an anti-segregation article. Several hundred more died in East St. Louis (Missouri in 1917) when a rumour spread that a black worker had spoken to a white woman at a union meeting. In Elaine (1919 in Arkansas) the trigger for the death of more than 200 blacks, also with women and children among them, was a labour claim by the pickers in the fields of the white landowners. And in Tulsa, (1921 in Oklahoma) it all started when a group of white people tried to lynch a young black man they accused of stealing. Up to 300 people died and 8,000 lost their homes when the angry white population set fire to Black Wall Street and the surrounding black neighbourhood.” (https://www.lavanguardia.com/internacional/20200603/481582308546/violenc...)
The system of racial segregation was reinforced by a half-illegal militia, the Ku Klux Klan, that persecuted black workers and inflicted savage torture on them in ritual acts. Officially dissolved in 1871, it reappeared in 1915 and is still preserved through local groups that defend a xenophobic, white supremacist and racist ideology. The big American democratic parties have occasionally openly encouraged these blatantly barbaric expressions of capitalism; at other times they have expressed their “outrage” about them, to favour the trap of “anti-racism”, yet they have always tolerated them as a complementary means to keep the working class divided.
The struggle of the workers’ movement against slavery
When slavery in the US was at its height, Marx (1860) described the life of the proletarians in England,  an atrocious “life” as Engels had already described it in his famous book in 1845 . No doubt the life of the proletarians in those times was as miserable and exhausting as that of many slaves. But it is not the same, for the future of the revolutionary class, the exploitation of slavery as “the existence of the free wage-labourer, who sells his labour power to capital”. The proletariat experiences a new form of exploitation that contains the possibility, if it is able to develop a conscious struggle, of overcoming the contradictions of capitalism by installing a communist society. The exploitation of the proletariat entails a universal suffering encompassing all forms of oppression and exploitation that have existed in class societies and that, consequently, can only be resolved by a universal revolution going to the roots of all the exploitation and oppressions that exist in capitalism and, therefore, in all class societies.  That's why one of the aspects of the working class struggle had to be the fight against slavery, especially in a country like the US.
In view of the situation of the American Civil War, the IWA (International Workers Association, First International), did not hesitate to send a message of support, written by Marx, to the Northern States led by Lincoln. It was not a question of supporting one faction of the bourgeoisie against another reactionary class (the big landowners of the South) . Marx rightly thought that the end of slavery would give a boost to the unification of the working class. And so in Capital (written at the same time as the end of the Civil War in the US and the “official” end of slavery, 1865)he establishes a link with the struggle for the 8 hour day: “In the United States of North America, every independent movement of the workers was paralysed so long as slavery disfigured a part of the Republic. Labour cannot emancipate itself in the white skin where in the black it is branded. But out of the death of slavery a new life at once arose. The first fruit of the Civil War was the eight hours’ agitation, that ran with the seven-leagued boots of the locomotive from the Atlantic to the Pacific, from New England to California.” (Capital, Volume I, “The working day”, Section 2: “The greed for surplus labour. Manufacturer and boyard”).
What about the working class in America?
Both Marxists and anarchists clearly put forward the unity of the working class, whatever its colour. This tradition took shape at the beginning of the 20th century in the IWW, the well-known revolutionary industrial union in the US, which was formed on the basis of an internationalist policy, against war and obviously for the unification of the working class, whatever its colour.  We already know the limits of revolutionary unionism and the failure of the IWW. But, in the worker's memory will remain “The experience of the IWW, the exemplary courage of its militants in the face of a ruling class for whom no violence or hypocrisy was too vile, is thus a reminder that the workers of America are indeed the class brothers of workers the world over, that their interests and struggles are the same, and that internationalism is not a vain word for the working class, but the touchstone of its very existence. The divisions between native-born, English-speaking workers (even if the latter were only second generation immigrants themselves) and newly arrived immigrant workers who spoke and read little or no English had long been a cause for concern in the workers’ movement in the US. In a letter to Sorge in 1893, Engels warned against the bourgeoisie’s cynical use of divisions within the proletariat, which retarded the development of the workers’ movement in the US. The bourgeoisie skilfully used race, ethnic, nationality and linguistic prejudices to divide workers amongst themselves, and to disrupt the development of a working class that saw itself as a united class. These divisions were a serious handicap for the working class in the US because it cut off the native Americans from the vast experience gained by workers in Europe and made it difficult for class conscious American workers to keep up to date with the international theoretical developments within the workers’ movement.” (“The IWW: The failure of revolutionary syndicalism in the USA, 1905-1921”; International Review no.124 - 1st quarter 2006)
In a letter of December 2, 1893, Engels replied to a question by Friedrich Adolf Sorge about the absence of a significant socialist party in the US, explaining that “There is no denying that conditions in America present considerable and peculiar difficulties to the steady growth of a labour party”. Among these difficulties, one of the most important was “immigration, which splits the workers into two groups, native-born and foreign, and the latter again into 1. Irish, 2. Germans, 3. a number of smaller groups, each speaking only its own language - Czechs, Poles, Italians, Scandinavians, etc. And, in addition, the negroes. To form a party of one’s own out of all these calls for exceptionally strong incentives. Every now and again a powerful élan may suddenly make itself felt, but all the bourgeoisie has to do is to stick it out passively, whereupon the dissimilar working-class elements will disintegrate again.” (http://www.koorosh-modaresi.com/MarxEngels/V50.pdf)
Black workers, who had already begun to flee to the North during slavery (when even in those states they could be persecuted and sent back to the South), began to go to the industrial zones especially from the beginning of the 20th century. And this “division” that Engels speaks of was reflected in the appearance of ghettos, a trend that was accentuated with the counter-revolution. The abominable ignominy of “modern” slavery had the particularity of its “unique” “racial” origin (sub-Saharan Africa, as opposed to ancient, Medieval or Eastern slavery where the slave could be of very different origins) so that newly proletarianised former slaves were immediately seen as having just come out of their commodity-object status. The US bourgeoisie, on the other hand, prohibited until very recently “coloured” emigration, favouring in the great years of emigration to the US from the end of the 19th century until the 1930s, the European populations. It is true that the existence of “ethnic” neighbourhoods is a “tradition” in the urban habitat in the US, but with the black ghettos the separation was much more clear-cut.
Civil rights and police brutality
Racial segregation was officially abolished in 1964, a century after the abolition of slavery. The idea was to give a channel to a growing sector of the black bourgeoisie that was being hindered in their business by these laws. The “great fruit” of the Civil Rights Laws was the promotion of black people to the upper echelons of politics and business. In the Bush administration, Colin Powell, the butcher of Iraq, and Condoleezza Rice, secretary of state, stood out, with the high point being Obama's election in 2008 as the first black president.
However, for black workers nothing changed. They continued to be victims of police and judicial discrimination that makes a black person seven times more likely to end up in prison than a white person.
Especially cruel is the treatment of black people by the police, even though there are many more black police officers. The 1992 Los Angeles crime that sparked violent protests was horrible. During Obama's term there were more police killings than ever before .
The murder of Georges Floyd on May 26 at the hands of four Minneapolis police officers was a tragic further demonstration of this continuation of official ruling class violence. The dominant classes, through their states, have a monopoly on violence. They exercise it in general to impose their domination, especially against the working class. Alongside the “official” forces of order, there are militias, more or less illegal armed groups. Over the years, the US has become a paradigm of the most extreme violence. And in many other countries this extreme official, unofficial or illegal violence (take the “example” of Mexico) has been established to last as long as this criminal system lasts. All these scourges are old, yes, but the trend of this model has become general, it is sharpened in all corners of the planet. We are living today through the decomposition of the capitalist system and all that official, unofficial or illegal criminal violence is on the march. Whether we are ruled by democracies or dictatorships, by single or pluralistic parties, everyday life is marked by the growing violence of a criminal system, capitalism.
In the face of such outrages, very widely known this time thanks to the images of Floyd's agony transmitted by the whole world, people of all races and conditions took to the streets in outrage to end up demanding... a more democratic police, demanding the executioner to be more humane. On the one side, Trump throwing more wood on the fire, encouraging supremacists who are willing to shoot everyone that is not white; on the other side, the Democratic (and many Republican, like former President Bush) factions of the American political spectrum take the knee, calling on outraged artists and stars, supporting “patriotic” demonstrations (as the New York Times described the Black Lives Matter marches).
The fight for the unity of the working class
With the counter-revolution, from the 1930s onwards, the killings, the lynchings multiplied. In the Depression of 1929, the white petty bourgeoisie - well manipulated by the media that took advantage of its narrow search for scapegoats - attributed the crisis to “the Negroes”, “In Harlem, New York, there were an undetermined number of deaths and more than a hundred injured, in addition to numerous lootings, as a result of the alleged robbery of a young Negro in a white man's store. It was the first modern-day riot because it completely destroyed the shops. From then on, Harlem suffered episodes of almost continuous racial violence until the 1960s.” (https://www.zinez.net/internacional/20200603/481582308546/violencia-raci...)
In reality, the stain of slavery that had sullied capitalist development in the US and elsewhere ended up creating a barrier in workers' struggles in the US that has been difficult to break through.
This barrier has been raised higher by the social process of capitalist decomposition . This involves a putrefaction of social relations, a fragmentation of society into ethnic, religious, localist, or “affinity” groups, that lock themselves in their own small ghettos to give themselves a false sense of community, of protection from a more and more inhuman world. This tendency favours the division in the ranks of the workers - accentuated to the point of paroxysm by the poisonous action of parties, unions, institutions, propaganda, etc. - into “communities” of race, religion, national origin etc. To add more fuel to the fire of racial and linguistic divisions in the US proletariat, the emigration of workers from Latin America, which became massive from the 1970s, has been used by the bourgeoisie to create more ghettos, to subject immigrant workers to illegality and to push down the living conditions of all workers .
However, some workers’ struggles in the last 50 years have crossed that barrier: Detroit 1965, the Chrysler wildcat strike in 1968, the Post Office wildcat strike in 1970, the New York subway in 2005, the Oakland strike during the Occupy movement in 2011... Despite their limits, these struggles are an experience from which we can draw lessons in the struggle for class unity.
In the 19th century fighting against slavery was fighting for the working class. Today, the brutality of the police, the white supremacists and the state in general (and its prisons) on the one hand, and the anti-racist movements on the other, serve to divide the working class and transform its most oppressed layers into an entirely separate population. Racism and anti-racism belong to the bourgeoisie. They are ideologies against the working class.
That's why the slogan of the proletariat is: We are neither white, nor black, nor any other color. We are a working class! As a banner in the protests against California's anti-immigrant law 187 said, WE ARE NOT COLOMBIANS, WE ARE NOT MEXICANS, WE ARE WORKERS.
 See the Series on the South African labour movement in our International Review https://en.internationalism.org/content/9459/history-class-struggle-south-africa; https://en.internationalism.org/international-review/201508/13355/south-africa-world-war-ii-mid-1970s; https://en.internationalism.org/international-review/201702/14250/soweto-1976-anc-power-1993; https://en.internationalism.org/content/16598/election-president-nelson-mandela-1994-2019
 See: “1492: The discovery of America” https://en.internationalism.org/internationalreview/200912/3406/1492-discovery-america
 The numbering of books or volumes, chapters and subchapters of Capital does not necessarily appear to be the same from one edition to another.
 The majority thesis of American historians of the 1970s was that the South lost because of an inefficient and unprofitable pre-capitalist system. For some years now, the majority thesis has been that the slave system was fully capitalist. It is difficult to know what these academics want to demonstrate; perhaps what they are looking for is to know which system has been more brutal, exploitative and inhumane. And therefore they use marxism, for which capitalism is first and foremost a social relation, the last class society to be overthrown in order to put an end to the exploitation of man by man. Thus, according to a well-known French historian, Nicolas Barreyre, speaking very recently about the system of the cotton farmers of the South of the United States, “In the 1970s, the dominant idea among historians, as among economists, was that the slave-owning South lived in an inefficient and unprofitable pre-capitalist economy that could not survive against the North, which had entered the industrial and capitalist revolution since the early 19th century. After the 2008 crisis, historians have once again become interested in the origins of the American economic system, forging what has been called the ‘new history of capitalism’. The idea is that the slave economy of the South was fully capitalist, which contributed to the rise of capitalism in the North” (Interview in Le Monde of 28/06/2020). We do not intend to make addenda to such eminent historians. The logic of the historians of the 1970s that the economy of the Southern States was “inefficient and unprofitable” because it was “pre-capitalist” seems to result from a rather vulgar version of “marxism”. Capitalism, at its height, made use of other non-capitalist economies for its expansion, both of markets and of sources of raw materials and capital. And until their full assimilation or destruction many of these economies were able to enrich themselves and serve the primitive accumulation of capital, especially when they belonged to the same nation. In the 19th century, throughout the world, there were systems not yet dominated by capitalism with which it did business, threatening them if necessary. See also https://en.internationalism.org/content/16709/american-civil-war-and-struggle-working-class-unity
 The hypocrisy of the English bourgeoisie knows no limits. On the one hand, it tolerated slavery in those countries that could serve it as allies and in those colonies where it suited its interests, while simultaneously turning itself into a “hammer against slavery” against rivals such as Spain, Portugal or Brazil, which did not have enough economic power to do without slavery, which they abolished very late (in 1886 in Spain and in 1888 in Brazil)
 It was one of the deadliest in history “630,000 people died. Even today, this figure is half of all the casualties the US has suffered in all the wars it has fought since, including Afghanistan.” https://www.lavanguardia.com/internacional/20200603/481582308546/violencia-racial-eeuu-historia-racismo.html?utm_source=newsletter&utm_medium=email&utm_content=claves_de_hoy
 Source already cited in note 6, unless otherwise indicated we refer to this source in subsequent quotations.
 Just read: “Capital, Volume I, Chapter 10: The Working day; Section 3: Branches of English Industry Without Legal Limits to Exploitation”, [a shocking chapter, with the example of children and the 15 hours of work for a seven year old child!]
 Condition of the Working. Class in England https://www.marxists.org/archive/marx/works/download/pdf/condition-worki...
 See: The principles of communism, in particular the points VI and VII https://www.marxists.org/archive/marx/works/1847/11/prin-com.htm
 “When an oligarchy of 300,000 slaveholders dared to inscribe, for the first time in the annals of the world, ‘slavery’ on the banner of Armed Revolt, when on the very spots where hardly a century ago the idea of one great Democratic Republic had first sprung up, whence the first Declaration of the Rights of Man was issued, and the first impulse given to the European revolution of the eighteenth century; when on those very spots counterrevolution, with systematic thoroughness, gloried in rescinding ‘the ideas entertained at the time of the formation of the old constitution’, and maintained slavery to be ‘a beneficent institution’, indeed, the old solution of the great problem of ‘the relation of capital to labor’, and cynically proclaimed property in man ‘the cornerstone of the new edifice’ — then the working classes of Europe understood at once, even before the fanatic partisanship of the upper classes for the Confederate gentry had given its dismal warning, that the slaveholders' rebellion was to sound the tocsin for a general holy crusade of property against labor, and that for the men of labor, with their hopes for the future, even their past conquests were at stake in that tremendous conflict on the other side of the Atlantic”. Address of the International Working Men's Association to Abraham Lincoln, President of the United States of America https://www.marxists.org/archive/marx/iwma/documents/1864/lincoln-letter.htm)
In 1864, more than 150 years ago, when the working class was still affirming itself as a class for the transformation of society, its organisations supported and had to support fractions of the bourgeoisie that were fighting against the - still important and strong - remnants of old systems of exploitation. Today, the reason that communists reject support for “democratic republics”, “human rights” and other bourgeois slogans is not that they are slogans “from another epoch”, but that they are, above all, hoaxes and weapons against the proletariat. And that's since the advent of decaying capitalism.
 See the report Racial conflicts in the Obama era, https://www.vozpopuli.com/internacional/Barack_Obama-Racismo-Estados_Unidos-racismo-estados_unidos-obama-conflicto_racial-matanzas-negros_0_933206737.html
 See our “Theses on Decomposition”, https://en.internationalism.org/ir/107_decomposition
 See: "’Latino’ demonstrations in the USA: Yes to the unity of the working class! No to unity with the exploiters!” https://en.internationalism.org/icconline/200605/1778/latino-demonstrati...