(1978-92), in the history of Afghanistan, the internal conflict between anticommunist Muslim guerrillas and the Afghan communist government (aided, from 1979 to 1989, by Soviet troops). The roots of the war lay in the overthrow of the centrist Afghanistan government in April 1978 by left-wing military officers, who then handed power over to two Marxist-Leninist political parties, the Khalq ("Masses") and Parcham ("Flag"), who together had formed the People's Democratic Party of Afghanistan. Having little popular support, the new government forged close ties with the Soviet Union, launched ruthless purges of all domestic opposition, and began extensive land and social reforms that were bitterly resented by the devoutly Muslim and largely anticommunist population. Muslim tribal-based insurgencies arose against the government, and these uprisings, along with internal fighting and coups between the Khalq and Parcham governmental factions, prompted the invasion of the country by about 30,000 Soviet troops in December 1979 with the aim of propping up the Soviet Union's new but faltering client state. The rebellion of the Muslim rebels, or mujahideen (literally, "strugglers"), grew in response, spreading to all parts of the country. The Soviets initially left the suppression of the rebellion to the Afghan army, but the latter was rapidly depleted by mass desertions and remained largely ineffective throughout the war.

The Afghan War quickly settled down into a stalemate, with about 100,000 Soviet troops controlling the cities, large towns, and major garrisons and the mujahideen roaming relatively freely throughout the countryside. The Soviet troops tried to crush the insurgency by various tactics, but the guerrillas generally eluded their attacks. The Soviets then attempted to eliminate the mujahideen's civilian support by bombing and depopulating the rural areas. Their tactics sparked a massive flight from the countryside; by 1982 some 2.8 million Afghans had sought asylum in Pakistan, and another 1.5 million had fled to Iran. The mujahideen were eventually able to neutralize Soviet air power through the use of shoulder-fired antiaircraft missiles supplied by the United States.

The mujahideen were fragmented politically into a handful of different groups, and their military efforts remained uncoordinated throughout the war. The quality of their arms and combat organization gradually improved, however, owing to experience and to arms shipments sent by the United States and other countries via Pakistan. In 1988 the United States, Pakistan, Afghanistan, and the Soviet Union signed an agreement for the withdrawal of Soviet troops and the return of Afghanistan to nonaligned status. In April 1992, various rebel groups, together with newly rebellious government troops, stormed the besieged capital of Kabul, and the communist president, Mohammad Najibullah, was ousted from power. A new transitional government, sponsored by various rebel factions, proclaimed an Islamic republic.