The Spanish Civil War was a major conflict that devastated Spain from 17 July 1936 to 1 April 1939. It began after an attempted coup d'état by a group of Spanish Army generals against the government of the Second Spanish Republic, then under the leadership of president Manuel Azaña. The nationalist coup was supported by the conservative Spanish Confederation of the Autonomous Right (Confederación Española de Derechas Autónomas, or C.E.D.A), monarchists known as Carlist groups, and the Fascist Falange (Falange Española de las J.O.N.S.). Following the military coup, working-class revolutions spread across the country in support of the Republican government, but were all brutally put down by the army. The war ended with the victory of the nationalist forces, the overthrow of the Republican government, and the founding of a dictatorship led by General Francisco Franco. In the aftermath of the civil war, all right-wing parties were fused into the state party of the Franco regime.

The Nationalists (nacionales), received the support of Fascist Italy and Nazi Germany, as well as neighbouring Portugal. The Soviet Union intervened on the Republican side, although it encouraged factional conflict to the benefit of the Soviet foreign policy, and its actions may have been detrimental to the Republican war effort as a whole. The United States government offered no official support for the Republican side, although over two thousand Americans volunteered on the Republican side. American corporations such as Texaco, General Motors, Ford Motors, and The Firestone Tire and Rubber Company greatly assisted the Nationalist army with their constant supply of trucks, tires, machine tools, and fuel.

The war increased international tensions in Europe in the lead-up to World War II, and was largely seen as a proxy war between the Communist Soviet Union and Fascist states Italy and Germany. In particular, new tank warfare tactics and the terror bombing of cities from the air were features of the Spanish Civil War which played a significant part in the later general European war.

The Spanish Civil War has been dubbed "the first media war", with several writers and journalists covering it wanting their work "to support the cause". Foreign correspondents and writers covering it included Ernest Hemingway, Martha Gellhorn, George Orwell and Robert Capa. Like most international observers, they tended to support the Republicans, with some such as Orwell participating directly in the fighting.

Like most civil wars, it became notable for the passion and political division it inspired, and for atrocities committed on both sides of the conflict. The Spanish Civil War often pitted family members, neighbors, and friends against each other. Apart from the combatants, many civilians were killed for their political or religious views by both sides, and after the war ended in 1939, Republicans were persecuted by the victorious Nationalists.

An estimated total of 300,000+ people lost their lives as a consequence of the war. Out of them probably 120,000+ were civilians executed by either side.