The Communist Party of the United States of America (CPUSA) was established on this day in 1919. CPUSA provided legal aid to the Scottsboro Boys, helped poor Southern farmers form sharecropper unions, and promoted communist ideas within the U.S.

The party was established after a split in the Socialist Party of America following the Russian Revolution, and initially operated underground due to the Palmer Raids, a series of anti-immigrant, anti-labor, and anti-communist raids conducted by Attorney General A. Mitchell Palmer.

CPUSA was an early opponent of segregation and racial discrimination, giving legal aid to the Scottsboro Boys and helping poor black farmers in the South organize sharecropper unions. Because of this, the party had a strong presence in Alabama in the 1930s. This history is detailed in "Hammer and Hoe: Alabama Communists during the Great Depression" by historian Robin D.G. Kelley.

During World War II, CPUSA's unwavering support for the Soviet Union alienated other factions of the American left, leading to a decline in membership. CPUSA membership was around 66,000 in 1939, and nearly 20,000 members left the party over the next four years, in part due to the Molotov–Ribbentrop Pact between the Soviets and Nazi Germany, which compelled the party to back off militant anti-fascist rhetoric.

In 2008, CPUSA called the election of Barack Obama a "transformative triumph of a labor-led all peoples' movement". Although CPUSA does not run candidates under its own banner, its members do run for office - in 2019, CPUSA member Wahsayah Whitebird won a seat on the city council of Ashland, WI.