Using the praxis and persecution of William Edward Burghardt Du Bois as a case study, this article analyzes the ways in which anticommunism became a tool of investigating, policing, discrediting, and ultimately curtailing what I call “Radical Black Peace Activism.” During the Cold War, the U.S. state apparatus treated this form of activism as an anti-American, foreign-inspired threat to national security attributable to the Communist “peace offensive.” Radical Black Peace Activists linked the end of global conflict, disarmament, and non-proliferation with antiracism, anticolonialism, anti-imperialism, and socialism. They argued that progress and justice could only be realized through international cooperation and peaceful coexistence. In other words, they demanded a new world order that would displace the United States, and its relentless militarism, as the world’s police. The investigation, indictment, and defamation of W. E. B. Du Bois, which coincided with the intensification of the Korean War, is illustrative of how Radical Black Peace Activism was treated as a form of Soviet-backed subversion. Through anticommunism, the U.S. state apparatus deemed the use of anti-Black and antiradical repression imperative to its security, stability, and status as the global defender of freedom and democracy.