Maček became the leader of the party on 13 August 1928 following Radić's assassination.
He quickly became a main opponent of King Alexander and was arrested in April 1933 and sentenced to three years in jail for treason.

Maček was released following Alexander's assassination in 1934.
His stated aim during that period was to transform Yugoslavia from a unitary state, dominated by ethnic Serbs, into a new form of state organization in which Croatian statehood would be restored.
His ideas appealed to a majority of Croats, and the Croatian Peasant Party gradually gained popularity.
He nurtured close relations with other opposition parties in Yugoslavia and, although his coalition lost elections in 1938, it remained a force for reckoning.
His persistence and political skills finally paid off in August 1939 with Dragiša Cvetković in the Cvetković–Maček Agreement and the creation of the Banovina of Croatia (Banovina), a semi-autonomous entity which contained Croatia and large sections of today's Bosnia and Herzegovina.
HSS became part of the coalition government while Maček himself became deputy prime minister of Yugoslavia.
Maček became the leader of the party on 13 August 1928 following Radić's assassination. He quickly became a main opponent of King Alexander and was arrested in April 1933 and sentenced to three years in jail for treason.
Maček was released following Alexander's assassination in 1934. His stated aim during that period was to transform Yugoslavia from a unitary state, dominated by ethnic Serbs, into a new form of state organization in which Croatian statehood would be restored. His ideas appealed to a majority of Croats, and the Croatian Peasant Party gradually gained popularity. He nurtured close relations with other opposition parties in Yugoslavia and, although his coalition lost elections in 1938, it remained a force for reckoning. His persistence and political skills finally paid off in August 1939 with Dragiša Cvetković in the Cvetković–Maček Agreement and the creation of the Banovina of Croatia (Banovina), a semi-autonomous entity which contained Croatia and large sections of today's Bosnia and Herzegovina. HSS became part of the coalition government while Maček himself became deputy prime minister of Yugoslavia.
Vladko Maček