Also in Laos, the bombing of Laotian territory along the Ho Chi Minh Trail, in Southern Laos, had begun in 1965 and American air activities over Laos continued at a high level from 1965-1969 and peaked in 1970 and 1971. Citing the illegal presence of North Vietnamese troops in Laos, Nixon explained the rationale of the U.S. air operations as being to interdict the flow of supplies and men into South Vietnam and thereby avoid the heavy toll in American and allied lives. With the bombing of North Vietnam, Laos and Cambodia by the Nixon administration in 1970-1971, the Vietnam War had become, in the minds of many, a general Indochina war. And in fact the Vietnamization-program, in order to succeed, led to the expansion of American military activities into Cambodia, Laos and Thailand.