Normans were descendants of the Vikings. They were from actually from France. They invaded England in 1066.the feudal system in England was set up in 4 steps.1) castle-guard (the obligation of a vassal to serve in a castle garrison of the lord), 2) suit in court (the vassal's obligation to attend the lord's court, to give him counsel, and to help him judge disputes, 3) attendance in the lord's entourage (accompanying the lord when he travelled or attended the court of his lord--meant to increase the social status of the lord), 4) hospitality to the lord or to his servants.
William, duke of Normandy was the one who led them to victory. That was the main reason they were so successful. The other reasons were that they had updated weapons and the used the element of surprise. The Norwegian king Harald Hardrada invaded northern England in September 1066, was victorious at the Battle of Fulford, but Harold defeated and killed him at the Battle of Stamford Bridge on 25 September 1066. Within days, William landed in southern England. Harold marched south to confront him, leaving a significant portion of his army in the north. Harold's army confronted William's invaders on 14 October at the Battle of Hastings.
During the battles the Normans faced a lot of rebellions by the people and the army about why they disagree to their battles. And some of their allies refused to help them.