Beginning in the late 1950s, North Vietnam began to move troops into areas of eastern Laos in support of the Pathet Lao, and also as a defensive measure to protect their logistical support of the insurgency in South Vietnam. In September 1959, North Vietnam formed Group 959 in Laos with the aim of building the Pathet Lao into a stronger force in its guerrilla war aimed at overthrowing the Royal Lao Government. Group 959 openly supplied, trained and supported the Pathet Lao militarily.