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.[1][2][3][4]
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).
Carrhae was the worst Roman disaster, and Rome's darkest day, since the catastrophic Battle of Cannae in 216 BC some 163 years earlier.