Final answer:
Under President Nixon's Vietnamization policy, there was a significant reduction in U.S. troops in Vietnam, leading to fewer than 24,000 by 1972 and ending with the Paris Peace Accords in 1973.
Step-by-step explanation:
In 1968, President Richard M. Nixon initiated a policy known as Vietnamization, which was aimed at ending American involvement in the Vietnam War by transferring combat roles to South Vietnamese troops. While the exact number of troops from the beginning phase is not specified in the given information, it is known that the process eventually resulted in a substantial reduction of U.S. military personnel.
By 1972, just before the signing of the Paris Peace Accords in January 1973, this policy had led to a decrease in U.S. troops from peaks of over 500,000 in prior years to fewer than 24,000. The Paris Peace Accords marked the official end of U.S. military involvement in Vietnam, although peace was tenuous and North Vietnam eventually overtook the South by 1975.