In addition to being a war of might, the Spanish Civil War was a war of ideas. Posters like this one — in which a revolutionary fights off the snake of fascism — were created by the hundreds to help inspire uprising.

They joined thousands of other people willing to risk their lives to preserve the Spanish Republic, which in 1936 was governed by the Popular Front, a diverse group of communists, liberals, socialists, Marxists, and anarchists. "Republican loyalists" waged a brutal war with Spanish Nationalists led by General Francisco Franco.

The Second Republic of Spain formed in 1931 after its last monarch, King Alfonso XIII, was deposed. The early years of the new republic were stressful, as socialists became increasingly active in the government. In the 1933 elections, socialists lost power, pushed out by reactionary landowners fearful of land reform and street violence. Worker and peasant strikes erupted. General Francisco Franco, chief of staff of Spain's armed forces, helped to put down the strikes. Franco was concerned that foreign socialists and communists were conspiring to gain a foothold in Spain. Leftists, he discovered, had infiltrated even Spain's army.

The victory of the Popular Front in 1936 brought new levels of social tension. In May 1936, communists took over factories and anarchists began calling for peasant revolts. Revolutionary rhetoric and street violence between communists and fascist youth gangs alarmed conservative elements in Spanish society.

Many spanish towns and innocent villagers were killed during the air bombings of the Spanish Civil War. This photograph was taken during an evacuation of villagers from Guadalajara in 1937.

Civil war began on July 17 when rebellious army forces attempted to unseat the Popular Front. They quickly took southern and western Spain, but they stalled in the north and east, failing to secure the large cities of Madrid and Catalonia. Franco returned from the Canary Islands on July 19 to join the rebellion. In September, he was named to lead the government of the nationalists, who comprised Spanish aristocrats, leaders of the military and the Roman Catholic Church, and members of the fascist Falange Party.

Franco immediately pressed Italy and Germany for military assistance, which helped to turn the tide of the war. Germans sent an experimental aircraft-tank unit called the Condor Legion as well as tanks and anti-aircraft guns. The German's horrific 1937 bombing of the Basque town of Guernica was memorialized in Pablo Picasso's famous painting of the same name.

Italians supplied the bulk of the foreign aid, nearly 50,000 men, tanks, aircraft, artillery, and other materiel. At 33, Franco had become the youngest general in Europe. In addition to German and Italian aid, his understanding of air-support, logistics, signals, and cartography made a significant difference in the war.

France and Russia sent aircraft to the Popular Front, neutralizing Franco's new air power. Russian tanks in Madrid prevented an army takeover there. Helped by Soviet organizers, about 20,000 volunteers from around the world swarmed to support the Loyalists, most of them arriving from France, Germany, Austria, Poland, Britain and the United States to form the International Brigade. Nearly half of these volunteers died in the fighting.

Francisco Franco ruled Spain as its sole dictator from 1938 until his death in 1975. Here, Franco reviews his troops.

Popular Front unity began to unravel in 1937 when communists and anarchists began to shoot at members of the Marxist party. In 1938, Stalin pulled his support and Franco's victory was assured. Barcelona fell to Franco in January 1939, Madrid two months later.

For fascist Germany and Italy, the war proved to be an excellent training ground for its new weapons of war and ideology. It was the first war in history where air power made a difference, as nearly 10,000 people died in air raids. For Spaniards, it was a devastating conflict. Roughly 200,000 deaths resulted. This included 100,000 Spanish civilians, most of them murdered when both sides committed atrocities. The loyalists targeted church leaders, and nationalists murdered Popular Front politicians, teachers, and doctors.