Defensive war

A defensive war is one of the causes that justify war by the criteria of the Just War tradition. It means a war where at least one nation is mainly trying to defend itself from another, as opposed to a war where both sides are trying to invade and conquer each other.

Examples

 * The Darius's invasions during the Greco-Persian Wars. Greeks were defending their homeland from the Persians.
 * Various invasions in World War II, such as the Invasion of Poland, the Battle of France, and the Battle of Britain and the Second Sino-Japanese War were offensive wars.