The second republic, proclaimed after the fall of the monarchy in 1931, was at first dominated by middle-class liberals and moderate socialists, among them Niceto Alcalá Zamora, Francisco Largo Caballero, and Manuel Azaña. They began a broad-ranging attack on the traditional, privileged structure of Spanish society: Some large estates were redistributed; church and state were separated; and an antiwar, antimilitarist policy was proclaimed. With their interests and their ideals threatened, the landed aristocracy, the church, and a large military clique, as well as monarchists and Carlists, rallied against the government, as did the new fascist party, the Falange.

The government's idealistic reforms failed to satisfy the left-wing radicals and did little to ameliorate the lot of the lower classes, who increasingly engaged in protest movements against it. The forces of the right gained a majority in the 1933 elections, and a series of weak coalition governments followed. Most of these were under the premiership of the moderate republican Alejandro Lerroux, but he was more or less dependent on the right wing and its leader José María Gil Robles. As a result many of the republican reforms were ignored or set aside. Left-wing strikes and risings buffeted the government, especially during the revolution of Oct., 1934, while the political right, equally dissatisfied, increasingly resorted to plots and violence.

When the electoral victory (1936) of the Popular Front (composed of liberals, Socialists, and Communists) augured a renewal of leftist reforms, revolutionary sentiment on the right consolidated. In July, 1936, Gen. Francisco Franco led an army revolt in Morocco. Rightist groups rebelled in Spain, and the army officers led most of their forces into the revolutionary (Nationalist or Insurgent) camp. In N Spain the revolutionists, under Gen. Emilio Mola, quickly overran most of Old Castile, Navarre, and W Aragon. They also captured some key cities in the south.

Catalonia—where socialism and anarchism were strong, and which had been granted autonomy—remained republican (Loyalist). The Basques too sided with the republicans to protect their local liberties. This traditional Spanish separatism asserted itself particularly in republican territory and hindered effective military organization. By Nov., 1936, the Nationalists had Madrid under siege, but while the new republican government of Francisco Largo Caballero (to which the anarchists had been admitted) struggled to organize an effective army, the first incoming International Brigade helped the Loyalists hold the city.

The International Brigades—multinational groups of volunteers (many of them Communists) that were organized mostly in France—represented only a small part of the foreign participation in the war. From the first and throughout the war, Italy and Germany aided Franco with an abundance of planes, tanks, and other materiel. Germany sent some 10,000 aviators and technicians; Italy sent large numbers of volunteers, probably about 70,000. Great Britain and France, anxious to prevent a general European conflagration, proposed a nonintervention pact, which was signed in Aug., 1936, by 27 nations. The signatories included Italy, Germany, and the USSR, all of whom failed to keep their promises. The Spanish republic became dependent for supplies on the Soviet Union, which used its military aid to achieve its own political goals.

As the war progressed the situation played into the hands of the Communists, who at the outset had been of negligible importance. The Loyalists ranks were riven by factional strife, which intensified as the Loyalist military position worsened; among its manifestations was the Communists' suppression of the anarchists and the Trotskyite Partido Obrero de Unificacion Marxista (POUM). On the Nationalist side internal conflict also existed, especially between the military and the fascists, but Franco was able to surmount it and consolidate his position. Gradually the Nationalists wore down Loyalist strength. Bilbao, the last republican center in the north, fell in June, 1937, and in a series of attacks from March to June, 1938, the Nationalists drove to the Mediterranean and cut the republican territory in two. Late in 1938, Franco mounted a major offensive against Catalonia, and Barcelona was taken in Jan., 1939. With the loss of Catalonia the Loyalist cause became hopeless. Republican efforts for a negotiated peace failed, and on Apr. 1, 1939, the victorious Nationalists entered Madrid. Italy and Germany had recognized the Franco regime in 1936, Great Britain and France did so in Feb., 1939; international recognition of Franco's authoritarian government quickly followed.

For Germany and Italy the Spanish civil war served as a testing ground for the blitzkrieg and other techniques of warfare that would be used in World War II; for the European democracies it was another step down the road of appeasement; and for the politically conscious youth of the 1930s who joined the International Brigades, saving the Spanish republic was the idealistic cause of the era, a cause to which many gave their lives. For the Spanish people the civil war was an encounter whose huge toll of lives and material devastation were unparalleled in centuries of Spanish history.