During the Spanish Civil War, several countries followed a principle of non-intervention to avoid any potential escalation or possible expansion of the war to other states. That would result in the signing of the Non-Intervention Agreement in August 1936 and the setting up of the Non-Intervention Committee, which first met in September. Primarily arranged by the French and the British governments, the committee also included the Soviet Union, Fascist Italy, and Nazi Germany. Ultimately, the committee had the support of 27 states.

The international response to the Spanish Civil War included many non-Spaniards participating in combat and advisory positions. The governments of Italy, Germany and, to a lesser extent, Portugal contributed money, munitions, manpower and support to the Nationalist forces, led by Francisco Franco. Some nations that declared neutrality favored the nationalists indirectly. The governments of the Soviet Union and, to a lesser extent, France and Mexico, aided the Republicans, also called Loyalists, of the Second Spanish Republic. The aid came even after all the European powers had signed a Non-Intervention Agreement in 1936. Although individual sympathy for the plight of the Spanish Republic was widespread in the liberal democracies, pacifism and the fear of a second world war prevented them from selling or giving arms. However, Nationalist pleas were answered within days by Adolf Hitler, Benito Mussolini and António de Oliveira Salazar. Tens of thousands of individual foreign volunteers travelled to Spain to fight, the majority for the Republican side.