2. To prevent the spread of communism. The US feared that if North Vietnam won the war, communism would spread to other countries in Southeast Asia. By intervening in Laos and Cambodia, the US hoped to prevent this from happening.
3. To support the governments of Laos and Cambodia. The US-backed governments of Laos and Cambodia were struggling to fight against communist insurgents. By providing military aid and support, the US hoped to help these governments stay in power.
The US intervention in Laos and Cambodia ultimately failed to achieve its goals. North Vietnam won the Vietnam War, and communism did spread to other countries in Southeast Asia. The US also suffered heavy casualties in Laos and Cambodia, and its involvement in these countries contributed to the growing unpopularity of the Vietnam War at home.