The shortest war in history lasted 22 minutes - Apparently.
In 1896, British and Irish forces clashed on the Irish island of Inishowen, but the conflict was quickly resolved after the British commander realized that the Irish forces were all relatives of his own soldiers. The "War" was ended with a handshake between the commanders, and both sides retreated without firing a shot. This brief skirmish has been recognized by historians as the shortest war in recorded history, and is still remembered today in Ireland.