Vietnamization

Wikipedia:

The goal was to gradually build up the South Vietnamese Army so that it could fight the war on its own. This policy became the cornerstone of the so-called "Nixon Doctrine". As applied to Vietnam, the doctrine was called "Vietnamization". The stated goal of Vietnamization was to enable the South Vietnamese army to increasingly hold its own against the NLF and the North Vietnamese Army. The unstated goal of Vietnamization was that the primary burden of combat would be returned to ARVN troops and thereby lessen domestic opposition in the U.S to the war.

During this period, the United States conducted a gradual troop withdrawal from Vietnam. Nixon continued to use air power to bomb the enemy, along with an US troop incursion in Cambodia. Ultimately more bombs were dropped under the Nixon Presidency than under Johnson's, while US troop deaths started to drop significantly. The Nixon administration was determined to remove US troops from the theater while not destabilizing the defensive efforts of South Vietnam.