1066 was a pretty lousy year to be living in England. King Edward the Confessor’s death in January triggered a succession crisis that brought contenders from all over Europe to fight for the throne. The King of Norway, Harald Hardrada, assembled a fleet of 300 ships carrying as many as 15,000 troops to invade. He arrived off the coast in September and was joined by Tostig Godwinson, the brother of Harold Godwinson, the man who’d recently been elected King of England. Tostig and Hardrada’s forces defeated a northern English army outside York on September 20, and York itself fell shortly after.
King Harold Godwinson, meanwhile, was busy in the south, awaiting an expected invasion from France by William, Duke of Normandy. When he heard about the chaos up north he hurried his army to Yorkshire, arriving there in only four days and taking the Norwegian army completely by surprise. The Norwegians were at a huge disadvantage, as their army was divided in half and most of the soldiers had left their armor behind on their ships, due to the warm weather. The English army annihilated them, and Tostig and Hardrada were among those killed.
King Harold accepted a truce with the surviving Norwegians, allowing them to leave so long as they promised never to attack England again. Just three days after the battle, the Duke of Normandy landed on the south coast, and Harold had to rush his army back south and lead them into battle again. He was defeated on October 14 at the Battle of Hastings, and the Norman Conquest of England began, right on the heels of the end of the Viking invasion.