to the National Assembly. In July 1925, after HSS had joined the government, Maček was released. HSS leadership and Banovina of Croatia 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. World War II This triumph proved to be short-lived as Banovina collapsed along with Yugoslavia when it was invaded by the Axis invasion in April 1941. Seen by Nazi Germany as an ideal leader of a new Axis puppet state—the Independent State of Croatia—Maček was offered the opportunity to become prime minister, but refused the offer twice. He called on the supporters of HSS to respect and co-operate with the new regime of Ante Pavelić, while at the same time delegating Juraj Krnjević to represent the Croatian people in the Yugoslav government-in-exile. Maček's strategy proved to be detrimental both for his party and himself. In October 1941 he was arrested and interned in Jasenovac concentration camp where he was put under the watch of Ljubo Miloš for some time. Five months later, on 16 March 1942, he was placed under house arrest together with his family at his home in Kupinec. His family shared his internment first in Kupinec, then two months of 1943 (9 January to 9 March) in Luburić's Zagreb apartment (which they shared with Luburić's aged mother and his two sisters), and finally from 9 December 1943 until the collapse of Pavelić's Ustaša regime in May 1945 in his Prilaz