Vietnam War (1955-1975)

The Vietnam War killed approximately 3.5 million people and marked the first major military defeat in American history, ending with North Vietnam's unification under communism despite overwhelming US firepower. This conflict outpaced #8 Korean War in its long-term domestic impact, producing the War Powers Act (1973) that limited presidential war-making, ending the military draft in 1973, and causing a 25% drop in public trust in government — from 76% in 1964 to 51% by 1975. The resulting cautious interventionism shaped US foreign policy until the Gulf War, with total US military spending of $168 billion (in 1974 dollars) — 2.3% of annual GDP.