The Spanish Civil War broke out in 1936: on 17 and 18 July, part of the military carried out a coup d’état that triumphed in only part of the country. The situation led to a civil war, in which the territory was divided into two zones: one under the authority of the Republican government, that counted on outside support from the Soviet Union and Mexico (and from International Brigades), and the other controlled by the putschists (the Nationalist or rebel faction), most critically supported by Nazi Germany and Fascist Italy. The Republic was not supported by the Western powers due to the British-led policy of non-intervention. General Francisco Franco was sworn in as the supreme leader of the rebels on 1 October 1936. An uneasy relationship between the Republican government and the grassroots anarchists who had initiated a partial Social revolution also ensued.

The civil war was viciously fought and there were many atrocities committed by all sides. The war claimed the lives of over 500,000 people and caused the flight of up to a half-million citizens from the country. On 1 April 1939, five months before the beginning of World War II, the rebel side led by Franco emerged victorious, imposing a dictatorship over the whole country. Thousands of men and women were imprisoned after the civil war in Francoist concentration camps, with approximately 367,000 to 500,000 prisoners being held in 50 camps or prisons.

The regime remained chiefly “neutral” from a nominal standpoint in the Second World War (it briefly switched its position to “non-belligerent”), although it was sympathetic to the Axis and provided the Nazi Wehrmacht with Spanish volunteers in the Eastern Front. The only legal party under Franco’s dictatorship was the Falange Española Tradicionalista y de las JONS (FET y de las JONS), formed in 1937 upon the merging of the Fascist Falange Española de las JONS and the Carlist traditionalists and to which the rest of right-wing groups supporting the rebels also added. The name of “Movimiento Nacional”, sometimes understood as a wider structure than the FET y de las JONS proper, largely imposed over the later’s name in official documents along the 1950s.

After World War II Spain was politically and economically isolated, and was kept out of the United Nations. This changed in 1955, during the Cold War period, when it became strategically important for the US to establish a military presence on the Iberian Peninsula as a counter to any possible move by the Soviet Union into the Mediterranean basin. In the 1960s, Spain registered an unprecedented rate of economic growth which was propelled by industrialisation, a mass internal migration from rural areas to Madrid, Barcelona and the Basque Country and the creation of a mass tourism industry. Franco’s rule was also characterised by authoritarianism, promotion of a unitary national identity, National Catholicism, and discriminatory language policies.