Red Terror is the name given by historians to various acts of violence committed from 1936 until the end of the Spanish Civil War by sections of nearly all the leftist groups involved. News of the rightist military coup in July 1936 unleashed a politicidal response, and no Republican controlled region escaped systematic and anticlerical violence, although it was minimal in the Basque Country. The violence consisted of the killing of tens of thousands of people, attacks on the Spanish nobility, small business owners, industrialists, and politicians and supporters of the conservative parties or the anti-Stalinist Left, as well as the desecration and arson attacks against monasteries, convents, Catholic schools, and churches.

The Spanish Civil War was a military conflict fought from 1936 to 1939 between the Republicans and the Nationalists. Republicans were loyal to the left-leaning Popular Front government of the Second Spanish Republic, and consisted of various socialist, communist, separatist, anarchist, and republican parties, some of which had opposed the government in the pre-war period. The opposing Nationalists were an alliance of Falangists, monarchists, conservatives, and traditionalists led by a military junta among whom General Francisco Franco quickly achieved a preponderant role. Due to the international political climate at the time, the war had many facets and was variously viewed as class struggle, a religious struggle, a struggle between dictatorship and republican democracy, between revolution and counterrevolution, and between fascism and communism. According to Claude Bowers, U.S. ambassador to Spain during the war, it was the "dress rehearsal" for World War II. The Nationalists won the war, which ended in early 1939, and ruled Spain until Franco's death in November 1975.