In May, French military forces surrendered to the Viet Minh concluding the Battle of Dien Bien Phu. In July, a cease fire agreement was reached by the Geneva Accords dividing Vietnam into two provisional states at the 17th parallel of latitude. Ngô Đình Diệm became Prime Minister of South Vietnam and Ho Chi Minh became President of North Vietnam. Diệm overcame an early challenge to his rule from army leaders and the Hòa Hảo and Cao Đài religious sects. The United States pledged its support to the Diệm government and began to replace France as the principal foreign power involved in South Vietnam. China and the Former Soviet Union began to provide economic assistance to North Vietnam.