The extent of the American victory in Vietnam was not apparent at the time. American strategic objectives in Vietnam were complex, and evolved over time as leaders in Washington came and went and as the situation on the ground matured. In general however, it was clear that Vietnam itself was not worth fighting for except as a battleground in the far larger struggle against global communism. In Vietnam, America demonstrated to other allied countries that it was prepared to sacrifice blood and treasure in that struggle. Vietnam eventually fell, but the Free World alliance system scarcely quivered, and within two decades Communism had been consigned to the ashbin of history.
Some thought that Afghanistan would be the Soviet's Vietnam, but it was not. The contrast could not be more striking. The USSR began its invasion in 1979 to support its puppet prime minister, who failed to extend power much beyond Kabul. The Soviets deployed more than 100,000 troops to Afghanistan [a fraction of the 500,000 American troop level in Vietnam]. In 1989, the final Soviet troops withdrew from an embarrassing war in Afghanistan that was seen as a waste of lives and money.
The Soviet defeat in Afghanistan was an important turning point contributing to the collapse of the Soviet Empire. In 1988, President Gorbachev announced his intention to withdraw Soviet forces from Afghanistan. Over 15,000 Soviet troops were killed in Afghanistan in the 1980s, not even a third of the American losses in Vietnam. The last Soviet soldier left on 15 February 1989. The Berlin Wall came down on 09 November 1989, and with it crumbled the Soviet empire in Eastern Europe. The Soviet Union itself collapsed two years later, in December 1991.