The Vietnam War grew from the Indochina conflicts after France lost control of its Southeast Asian colony and Vietnam was divided in 1954 into communist North Vietnam and western-backed South Vietnam pending elections that were never held. Guided by containment, the U.S. increasingly supported South Vietnam as Ngo Dinh Diem's unpopular regime faced a growing communist insurgency by the Viet Cong, aided from the north along the Ho Chi Minh trail. Under John F. Kennedy, American military advisers and air involvement increased, and after the Gulf of Tonkin incidents in 1964, Lyndon Baines Johnson escalated the conflict with Operation Rolling Thunder and the deployment of large numbers of ground troops. The war became a costly war of attrition fought largely in jungles and small engagements, while official claims of progress were badly shaken by the Tet Offensive in 1968, which deepened a credibility gap between the U.S. government and the American public. As antiwar protest grew, Richard Nixon pursued Vietnamization, gradually withdrawing U.S. troops while shifting more fighting to South Vietnamese forces, even as he widened the war into Cambodia. A cease-fire was signed in 1973 and American troops left, but fighting resumed, Saigon fell to North Vietnamese forces in 1975, and Vietnam was unified under a single communist regime. The war killed more than 58,000 Americans and as many as six million Vietnamese civilians and soldiers, became one of America's longest, most controversial, and only unsuccessful wars, and led many Americans to question containment and the policies of their leaders.