Such an argument said, in effect, that black people had to be whipped up by radical foreigners in order to challenge the remnants of slavery in the Jim Crow South, and that without those outsiders, America was, to steal a phrase from the 2016 election, already great. The view also ignores that it was the black members of the Communist Party U.S.A., raised in such circumstances, who made it clear that their struggles for economic independence were bound up with the racist violence they faced from both the police and white supremacist groups.

Those black Communists often had to fight to hold their party accountable to its professed ideals when the party shifted its strategy toward courting white liberals. The debates that resurfaced during the 2016 election cycle, about the primacy of race or class in left-wing organizing, particularly around the primary campaign of Bernie Sanders, echoed these past battles.

In the 1930s, the party taught its members to discuss their problems using the language of exploitation. This language meant that people “understood that racism and what they called male chauvinism wasn’t simply people acting badly or being psychologically controlled or being ignorant,” Professor Kelley said. “It was about the benefits that they derived from exploitative relationships.”

That framework, which has been revisited today in platform documents like “A Vision for Black Lives,” argues that racism, at root, is not about hate between groups, but about the way power is held in society. And class, according to this analysis, is created by relationships of exploitation.

These arguments were championed by organizers like Claudia Jones, a black leader within the Communist Party U.S.A. and a journalist for its newspaper, The Daily Worker. According to Charlene Carruthers, the national director of Black Youth Project 100, Ms. Jones expounded the idea now known as intersectionality decades before that term became so ubiquitous that Hillary Clinton used it in a tweet on the campaign trail. For Ms. Jones, understanding the lives of black women and the economic and social position they occupied would create a better understanding of the system of capitalism as a whole. It followed, Ms. Carruthers explains, that black women’s work was central in the struggle to replace the system.

Within organized labor, particularly the Congress of Industrial Organizations in the 1940s, the Communist-led unions were consistently the leaders on racial and gender equality. Sometimes this clashed with the wishes of white male members, who occasionally went on strike against the inclusion of black members. With the eventual purge of such so-called red unions from the federation, the cause of antiracism slipped to the sidelines. Only in the past decade or so has it returned as a priority for some unions.

The Communist Party U.S.A.’s support for the nonaggression pact between Nazi Germany and the Soviet Union at the beginning of World War II — a seeming betrayal of its strong anti-fascist stance — splintered the party’s membership. Revelations after the war about Stalin’s crimes further damaged the party’s international prestige. For the most part, in the West, Communist parties never recovered from those blows. At the same time, the end of the war hastened the demise of the old European empires, and Communists often took leading roles in the new anticolonial movements.