The referendum was held on October 23, 1955, and Diem proclaimed the Republic of Vietnam on October 26. He had served as prime minister under the former emperor Bao Dai, then called a vote to remove him and won by a margin no honest count could show. The numbers were absurd. He took the title of president.
Diem was a devout Catholic in a Buddhist country, and he built a state on loyalists and family. His brothers ran the police and the army, and his brother Nhu led the feared secret apparatus that jailed communists and rivals alike, so fear kept him in place while the state grew narrow and closed. The split hardened.
The 1954 Geneva Accords had meant to reunify Vietnam by election, but Diem refused to hold the national vote, and the line at the seventeenth parallel turned into a border. The United States backed him as a bulwark against the north, and aid and advisers flowed in. The war took shape. The divide became a front line of the Cold War that drew in powers far from the region.
Diem ruled until 1963, when his own generals killed him in a coup the Americans let happen. His republic outlived him only a little. The decisions of October 1955 set the course that drew the United States into a long and losing war.