The Vietnam War was a long, costly armed conflict that pitted the communist regime of North Vietnam and its southern allies, known as the Viet Cong, against South Vietnam and its principal ally, the United States. The divisive war, increasingly unpopular at home, ended with the withdrawal of U.S. forces in 1973 and the unification of Vietnam under Communist control two years later. More than 3 million people, including 58,000 Americans, were killed in the conflict. There had been fighting in Vietnam for decades before the Vietnam War began. The Vietnamese had suffered under French colonial rule for nearly six decades when Japan invaded portions of Vietnam in 1940. It was in 1941, when Vietnam had two foreign powers occupying them, that communist Vietnamese revolutionary leader Ho Chi Minh arrived back in Vietnam after spending thirty years traveling the world. Once Ho was back in Vietnam, he established a headquarters in a cave in northern Vietnam and established the Viet Minh, whose goal was to rid Vietnam of the French and Japanese occupiers. Having gained support for their cause in northern Vietnam, the Viet Minh announced the establishment of an independent Vietnam with a new government called the Democratic Republic of Vietnam on September 2, 1945. The French, however, were not willing to give up their colony so easily and fought back. For years, Ho had tried to court the United States to support him against the French, including supplying the U.S. with military intelligence about the Japanese during World War II. Despite this aid, the United States was fully dedicated to their Cold War foreign policy of containment, which meant preventing the spread of Communism. This fear of the spread of Communism was heightened by the U.S. "domino theory," which stated that if one country in Southeast Asia fell to Communism then surrounding countries would also soon fall. To help prevent Vietnam from becoming a communist country, the U.S. decided to help France defeat Ho and his revolutionaries by sending the French military aid in 1950.