William the Conqueror: 1061 to 1066
Fearing that the campaigning season in England is now too short, you disband most of your troops, telling them to come back next spring. But this is a fatal delay: king Harold is victorious in defeating the army of Harald Hardrada of Norway, at a battle soon known far and wide as "Stamford bridge." His reputation is so great after killing the erstwhile greatest warrior in Christendom, that nobody wants to take him on next spring, or ever. Your chance to invade England is lost forever.
