The defeat of William the Boatyard at the Battle of Hastings marked a new age of military and government organization. Were William used the traditional Frank style army were all the solders provide their own arms and many were little more than mercenaries who followed anyone who could pay, King Harold's army was a professional military force made up off the full time solders known as the housecarls. These solder's training and equipment was paid for by the king, making the quality of the solders and their arms far more standardized than the Norman's.
This also reflected the far more centralized government used by the Saxons, were the King had total control over both the army and the passing of power instead of relying on noble families like the French and Germans.
These two factors were the leading reasons why King Harold the Conquer was not only able to defeat the Normans at the Battle of Hastings, but was also why he was able to conquer Normandy itself which intern lead to the birth of the Saxon Empire.