Why is the Spanish civil was called a proxy war?

The Spanish Civil War (1936-1939) is often referred to as a proxy war because it involved significant foreign intervention and support for both sides, reflecting broader ideological conflicts of the time. The Nationalists, led by Francisco Franco, received military and logistical support from Nazi Germany and Fascist Italy, while the Republicans were backed by the Soviet Union and international brigades composed of volunteers from various countries. This external involvement turned the conflict into a battleground for competing ideologies, particularly fascism versus socialism, making it a precursor to World War II.