Spanish Civil War - Wikipedia

On July 26, 1936, the Axis Powers decided to intervene in the Spanish Civil War. From the article:

"The coup was supported by military units in the Spanish protectorate in Morocco, Pamplona, Burgos, Zaragoza, Valladolid, Cádiz, Córdoba, and Seville. However, rebelling units in some important cities—such as Madrid, Barcelona, Valencia, Bilbao, and Málaga—did not gain control, and those cities remained under the control of the government. Spain was thus left militarily and politically divided. The Nationalists and the Republican government fought for control of the country. The Nationalist forces received munitions, soldiers, and air support from Nazi Germany and Fascist Italy, while the Republican (Loyalist) side received support from the Communist Soviet Union and leftist populist Mexico. Other countries, such as the United Kingdom, France, and the United States continued to recognize the Republican government but otherwise followed an official policy of non-intervention. Notwithstanding this policy, tens of thousands of citizens from non-interventionist countries directly participated in the conflict. They fought mostly in the pro-Republican International Brigades which also included several thousand exiles from pro-Nationalist regimes.

The Nationalists advanced from their strongholds in the south and west, capturing most of Spain's northern coastline in 1937. They also besieged Madrid and the area to its south and west for much of the war. After much of Catalonia was captured in 1938 and 1939, and Madrid was cut off from Barcelona, it was obvious to everyone that Republican military position was hopeless. Once Madrid and Barcelona were occupied without resistance, Franco declared victory and his regime received diplomatic recognition from all non-interventionist governments. Thousands of leftist Spaniards fled to refugee camps in southern France. Those associated with the losing Republicans were persecuted by the victorious Nationalists. With the establishment of a dictatorship led by General Franco in the aftermath of the war, all right-wing parties were fused into the structure of the Franco regime.[10]

The war became notable for the passion and political division it inspired and for the many atrocities that occurred, on both sides. Organized purges occurred in territory captured by Franco's forces so they could consolidate their future regime.[11] A significant number of killings also took place in areas controlled by the Republicans.[12] The extent to which Republican authorities took part in killings in Republican territory varied."