The migration boosted the Catholic power base of Diem; whereas the majority of Vietnam's Catholics previously lived in the north, now most were in the south. Fearing a communist victory, Diem cancelled the elections. Believing the northern Catholics to be a bastion of solid anti-communist support, Diem proceeded to treat his new constituents as a special interest group. In the long run, the northern Catholics never fully integrated into southern society and Diem's favoritism toward them caused tension that culminated in the Buddhist crisis of 1963, which ended with the downfall and assassination of the South Vietnamese leader.