Vietnam extremely changed the US foreign policy. Public protests and financial problems were important factors that drove Nixon to the withdrawal of the troops. Before Vietnam the main idea of USFP was confrontation and aactivities to increase the own sphere of influence. You may have heard about 'rollback' or the Truman doctrine; both explained American participation in the wars in Vietnam and Korea.

The Nixon doctrine delegated the responsibility for upcoming wars to the nation's were they would be fought; it promised financial support as well as armament supply, but no direct interventions, to befriended nations. In the following years nations like Iran (governed by the shah!) or Saudi Arabia were provided with arms.

But under Nixon detente was rising, too, which was a relaxation of tensions between east and west. On American side detente was indeed driven by the Vietnam fiasco; there were neither financial possibilities, nor public support for increasing the risk of escalation. Detente is mostly characterized with 'peaceful coexistence'.

Detente led to treaties to control the race of arms (like SALT) and and other agreements with the USSR (e.g. about how to react in case of a nuclear incident).

Another point is the Afghan war where the US supported islamist rebels; this is explained by the Reagan doctrine that stated support for rebellions in communist controlled countries. Detente had failed under carter and Reagan wanted to improve the American position, so he started to spend horrendous amounts of money in military issues.

Since the Vietnam war direct American interventions during the cold war were reduced to a minimum, but USfp supported others financially to fight against the communists. Under Nixon there was around a decade of relaxation between the superpowers.