Who fought on the side of the replublicans in the Spanish civil war

Those supporting the principles of the Republican Government in the face of Franco's fascist aggression.

Explanation:

Support from within Spain came from the left. This included, intellectuals, socialists and communists. The Republican movement was also supported by the International Brigade. These were volunteers from all over the world who went to Spain to fight fascism. One example is George Orwell who wrote about his experiences in Homage to Catalonia. Catalonia, and it's major city Barcelona was a Republican stronghold, and Catalonian culture was subsequently suppressed by Franco until his death. This reflects the regional element in support for the two sides in the Spanish Civil War.

Answer: Those supporting the principles of the Republican Government in the face of Franco's fascist aggression.