When William of Normandy became King William I of England after the Battle of Hastings in 1066, he was a conqueror with a very small army of foreign (French) soldiers. It was not at all certain that he could hold on to his newly-won kingdom.
William had to do something fast. He also had to pay off his barons who had lent him their troops. He did both things at the same time – by giving out land to the barons, and insisting they built castles on it and defended their land in his name.
