4. Soviet Invasion of Afghanistan (1979-1989)
The Soviet Union intervened in Afghanistan in December 1979 to support a friendly regime, deploying approximately 30,000 troops. Despite the significant military engagement, neither the Soviet Union nor Afghanistan issued a formal declaration of war. This conflict became a Cold War flashpoint, involving guerrilla fighting, foreign support for the Mujahideen, and devastating civilian impact (history.com).
