Following the introduction of U.S. Marines into South Vietnam in March 1965, there was a gradual buildup of U.S. forces. President Lyndon Johnson approved the presence of 200,000 servicepeople by the end of the year. The overall American goal was to use firepower to break the will of North Vietnam and its supporters and force them to negotiate on American terms. As the United States expanded its combat role, more and more North Vietnamese regulars poured into the South. These North Vietnamese regulars relied on South Vietnamese guerillas, or Vietcong, for support, as well as the local population in rural areas of the country.