The Vietnam War began as a conflict between North Vietnam and South Vietnam. The United States initially sent military advisors to support South Vietnam against North Vietnam and communist rebels. Over time, U.S. involvement escalated, with over 500,000 troops deployed by 1968. However, the Tet Offensive in 1968 shocked Americans and turned public opinion against the war. Protests against U.S. involvement grew as the war dragged on without clear progress. Peace negotiations began in 1973, and U.S. troops withdrew from Vietnam in 1975, with North Vietnam defeating South Vietnam and reunifying the country under communist rule.