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.

In the history of the 20th century, the interwar period lasted from 11 November 1918 to 1 September 1939 – from the end of World War I (WWI) to the beginning of World War II (WWII). It was relatively short, yet featured many social, political, military, and economic changes throughout the world. Petroleum-based energy production and associated mechanisation led to the prosperous Roaring Twenties, a time of social and economic mobility for the middle class. Automobiles, electric lighting, radio, and more became common among populations in the first world. The era's indulgences were followed by the Great Depression, an unprecedented worldwide economic downturn that severely damaged many of the world's largest economies.