The topic of this graduate thesis is The Croatian Peasant Party (Hrvatska seljačka stranka, HSS) between 1920. and 1929. The HSS, led by Stjepan Radić, was the leading Croatian party in the Croatian national movement in the newly founded Kingdom of Serbs, Croatians and Slovenes (SHS). The Kingdom of SHS was established on the 1st of December 1918. when the prince regent Aleksandar Karađorđević have proclaimed unified state without asking Croatians or other nationalities on the territory of the south Slavs. The state was administered centralistic and unionistic from Belgrade. The idea of the unified three nations was implemented, but in reality it was promoting the plans for Greater Serbia. The Radić brothers, Stjepan and Antun, founded the party near the end of 1904. under the name Croatian Peoples' Peasant Party (Hrvatska pučka seljačka stranka, HPSS). Antun was in charge of the party's ideology and developed the idea of peasant's movement. In the Austria-Hungary Empire the party had small number of representatives and it did not make much of a difference. After the fall of the Empire, the HSS and Radić at first supported the unification of the State of SHS with the Kingdom of Serbia, but with the federal and democratic principles. But, the Peoples' Council with Svetozar Pribičević at the helm wanted the faster unification and the state that was unitaristic and centralistic. The HPSS with Radić at the helm refused to recognize the Kingdom of SHS and its centralistic Vidovdan Constitution. The party between the 1920. and 1925. was called Croatian Peoples' Peasant Party and Stjepan Radić wrote the constitution of Neutral Peasants' Republic of Croatia. Radić changed his strategy often during his fight for Croatian equality in the joined state, so the party in the 1925. recognizes the Vidovdan Constitution, joined state and the Karađorđević dynasty. The Party for then on bears the name of the Croatian Peasant Party. After the failed attempt to form a coalition with the People's Radical Party, Radić joins a coalition with his former political opponent Svetozar Pribičević and his party. That formed the Peasants'-Democratic coalition (SDK). In the Peoples' Council the SDK fights hard for the equality and the revision of the constitution. At the beginning of the June of 1928. a member of the radical party Puniša Račić shoots at the members of the HSS and manages the wound Stjepan Radić who dies from the wounds at the 8th of August. His successor is Vladko Maček who continues to fight for the resolution of the Croatian question in the joined state. The King Aleksandar took an advantage of the situation and the on 6th of January 1929. he introduced personal dictatorship and changed the name of the state which from the Autumn of 103 1929. bears the name of the Kingdom of Yugoslavia, thus begins the new hard period for the Croatian people.