After a brief occupation by the Japanese at the end of World War II, which followed in a declaration of independence by Lao nationalists, the French reoccupied Laos and the rest of French Indochina, which included Vietnam and Cambodia. In the following insurgency, the Indochinese Communist formed the Pathet Lao, a Laotian nationalist movement, ally of the Vietnamese in the struggle against France. After the French defeat, the Geneva Accords of 1954 established Laos sovereignty. In 1960, civil war broke out between the Royal Lao Army, supported by the United States, against the Pathet Lao insurgents, supported by the Communists in North Vietnam. John F. Kennedy proposed a negotiated settlement with the Soviet Union and other interested parties. In 1962 a peace conference in Geneva produced a Declaration on the Neutrality of Laos and a three-part coalition government divided between pro-American, pro-Communist and neutral factions. The 14 signatories pledged to respect Laotian neutrality, to refrain from interference — direct or indirect — in the internal affairs of Laos, and to refrain from drawing Laos into military alliance or to establish military bases in Laotian territory. The Laotian government pledged to promulgate constitutionally its commitments which would have the force of law. However, the agreement was contravened almost immediately by the United States, the Soviet Union, the Peoples Republic of China, North Vietnam and the Pathet Lao themselves. Contrary to the agreement, North Vietnam continued to garrison 7000 soldiers in Laos, the Soviet Union and the Peoples Republic of China provided military support to the Pathet Lao, and the United States began a bombing campaign that supported both the Royal Laotian Government and their efforts in South Vietnam. Despite the cease fire, the Pathet Lao continued to attack and harass Neutral forces. This exemplified the conduct of all parties throughout the for the remainder of the Second Indochina War. In 1959 the Democratic Republic of Vietnam had already established a supply line through "neutral" Laotian territory for supplying the Viet Cong insurgency against the government of South Vietnam. It was called by the communists the "Trường Sơn Strategic Supply Route." Despite the 1962 International Agreement on the Neutrality of Laos, the Pathet Lao and North Vietnamese continued to use and improve the supply route which would become known as the Ho Chi Minh Trail. More specifically, during the Second Indochina War the North Vietnamese obtained the cooperation of the Lao People's Revolutionary Party in constructing and maintaining the Ho Chi Minh Trail which passed through the length of Laos. Thousands of Vietnamese troops were stationed in Laos to maintain the road network and provide for its security. Vietnamese military personnel also fought beside the Pathet Lao in its struggle to overthrow Laos' neutralist government. Cooperation persisted after the war and the Lao communist victory.
