A military disaster is the defeat of one side in a battle or war which results in the complete failure of the losing side to achieve their objectives. It often, but not always, involves a high and disproportionate loss of life. The causes are varied and include human error, inferior technology, logistical problems, underestimating the enemy, being outnumbered, and bad luck. Entries on this list are those where multiple sources dealing with the subject of military disasters have deemed the event in question to be a military disaster (or an equivalent term).

Ancient era

Medieval era

16th century

18th century

19th century

20th century

First World War

Second World War

Cold War era