By the late 1960s the nation's problems largely stemmed from conflicts brewing in neighboring Cambodia and Vietnam. Although Thailand had received $2 billion in U.S. economic and military aid since 1950 and had sent troops (paid by the U.S.) to Vietnam while permitting U.S. bombe bases on its territory, the collapse of South Vietnam and Cambodia in spring 1975 brought rapid changes in the country's diplomatic posture. At the Thai government's insistence, the U.S. agreed to withdraw all 23,000 U.S. military personnel remaining in Thailand by March 1976