Why did Ngo Dinh Diem refuse to go along with the planned elections of 1956 that were to unite Vietnam?

In 1954, the Vietminh forces of Vietnam defeated the French at the Battle of Dien Bien Phu, and the nation was temporarily divided into two sections, north and south. The people of the south chose Ngo Dinh Diem as their ruler and Ho Chi Minh ruled the north. Diem refused to go along with the planned elections in 1956 to unite the nation so the Vietminh members in the south created the Viet Cong and the war between north and south for control of the country began. Diem realized he would probably lose the elections. Many communists had moved south from the north and would probably not vote for Diem's regime. The US encourage Diem with aid and money. He was even considered a "George Washington of South Vietnam" by some of the American media. With US support, Diem felt he could defeat the communists so he declared a republic in South Vietnam. The government of South Vietnam requested military advisors from the United States to help train the South Vietnamese army. MrV