A proxy war is a war where two powers use third parties as a supplement or a substitute for fighting each other directly.

Proxy wars were common in the Cold War as the two nuclear-armed superpowers (Soviet Union and the United States of America) did not wish to fight each other directly, which ran the risk of escalation to a nuclear war. Proxies were used in conflicts in Afghanistan, Angola, Vietnam and many other states. Perhaps the largest current war by proxy is the Second Congo War in which the governments of the Democratic Republic of the Congo, Uganda and Rwanda are all using third party armed irregular groups.

While the superpowers have used whole governments as proxies, terrorist groups or other third parties are more often employed. It is hoped that these groups can strike an opponent without leading to full-scale war. Iran has used Hezbollah to this purpose to hit Israel and Pakistan has long used armed groups to advance its cause in Kashmir without going to war against India.

Proxy wars have also been fought alongside full-scale conflicts. During the Iran-Iraq War both nations armed factions in the Lebanese Civil War and pitted them against each other, for instance.

It is almost impossible to have a pure proxy war as the groups fighting for another power have their own interests, which are often divergent from those of their patron. For instance after the Soviet invasion of Afghanistan the groups the United States had been backing quickly turned and became the nucleus of the Taliban and al-Qaida.

A famous proxy war was the Spanish Civil War that saw an internal conflict become a battle between fascism and communism as Germany, Italy and the Soviet Union poured resources and advisors into the country. This proxy war served as a useful proving ground for the great powers to test equipment and tactics that would later be employed in the Second World War.