The National Liberation Movement in Croatia was part of the anti-fascist National Liberational Movement in the Axis-occupied Yugoslavia which was the most effective anti-Nazi resistance movement led by Yugoslav revolutionary communists during the Second World War. NOP was under the leadership of the League of Communists of Yugoslavia (KPJ) and supported by many others, with Croatian Peasant Party members contributing to it significantly. NOP units were able to temporarily or permanently liberate large parts of Croatia from occupying forces. Based on the NOP, the Federal Republic of Croatia was founded as a constituent of the Democratic Federal Yugoslavia.