Euzko Gudarostea was the name of the army commanded by the Basque Government during the Spanish Civil War. It was formed by Basque nationalists, socialists, communists, anarchists and republicans under the direction of lehendakari José Antonio Aguirre and coordinating with the army of the Second Spanish Republic. It fought the troops of Francisco Franco during 1936 and 1937. It surrendered to the Italian Corpo Truppe Volontarie at Santoña, while the rest of the Republican army kept fighting until 1939. This event is called the Santoña Agreement, Pact of Santoña, or Treason of Santoña by some Spanish leftists.

Basque nationalism is a form of nationalism that asserts that Basques, an ethnic group indigenous to the western Pyrenees, are a nation and promotes the political unity of the Basques, today scattered between Spain and France. Since its inception in the late 19th century, Basque nationalism has included Basque independence movements.