United States and South Vietnamese forces undertook a military invasion of Cambodia, launching Operation Rock Crusher to hunt down Viet Cong forces. The incursion was fueled by intelligence reports indicating that the Viet Cong and North Vietnamese troops were using the Cambodian border as a sanctuary to regroup and resupply. This offensive action took place across various regions of Cambodia, particularly in the border areas that had been refuges for combatants engaged in the Vietnam War.

The incursion was justified by U.S. officials as a necessary measure to protect South Vietnam and weaken the North Vietnamese forces. It marked a significant escalation of the Vietnam War as American troops moved into a neutral country, thereby intensifying anti-war sentiments back in the United States. Public protests erupted, and many questioned the legality and morality of invading Cambodia, while supporters argued it was essential to secure victory in Vietnam.

The invasion resulted in heavy combat, with fierce resistance from Viet Cong forces. The U.S. military reported significant successes in terms of enemy casualties and the destruction of supplies. However, it also caused civilian displacement and further complicated the geopolitical situation in the region. After the invasion, Cambodia would experience destabilization, ultimately leading to the rise of the Khmer Rouge.