they opposed it, hypocritically, because they believed that H* Chi Minh (the communist leader of North Vietnam) would win over Ngo Dinh Diem (leader of South Vietnam) and that the country would be united with a communist leader and therefore communist government. the United States' policy of containment and the domino theory attributed to their intervention in cancelling the elections because they believed that if Vietnam became communist that other countries specifically those in Southeast Asia would follow.