This essay explores the historical genealogy of Internal Colonialism as an American theory of race from approximately 1950 to the early 1990s. Internal Colonialism as an idea originated in Latin America as part of a larger Marxist critique of development ideologies and was specifically elaborated by dependency theorists to explain the racial effects of poverty and isolation on indigenous communities. Black and Chicano radicals fascinated by the Cuban Revolution learned about the theory by reading Ernesto “Che” Guevara, by participating in the Venceremos Brigades harvesting Cuban sugar cane, and by the larger diffusion of Latin American dependency theory in the United States. Black nationalists and Chicano radicals embraced, transformed, and further elaborated on the idea of Internal Colonialism to explain their own subordinate status in the United States, which was the product of forced enslavement and military occupation. As a colonized population in the United States, Blacks and Chicanos suffered the effects of racism, were dominated by outsiders, much as colonial subjects in the Third World, and had seen their indigenous values and ways of life destroyed. As a theory that explained the effects of racism, it had its greatest popularity during the radicalization of the Civil Rights Movement in the late 1960s and early 1970s when nationalism and separatist ideas were in vogue. By the 1980s the theory had been abandoned in favor of more accommodationist politics and ideas.