The thesis deals with the history of the Croatian Peasant Party (HSS) from 1939 to 1945, the period of foundation of the Banovina of Croatia and the Second World War. The leadership of the party decided not to side with the Ustasha or the Partisans. The policy of waiting and not joining the National Liberation War led to the division among the party members, resulting in the formation of the Croatian Republican Peasant Party (HRSS), with the help of the Communist Party of Croatia (KPH) and those members who did not support Maček. The Communist Party propagated changes to the benefit of workers and peasants, emphasizing federalism and republicanism, all of which was very close to HSS's underlying principles. This is why many of its members and supporters joined the National Liberation Army and the National Liberation Movement. HRSS, thanks to the actions of KPH, disappeared from the political scene in the same way it had emerged. Immediately after the war, in the restored Yugoslavia, KPH obstructed the work of the until recently most influential Croatian party, which resulted in its disappearing from the political scene.