Describe the Border Wars between England and Wales in the High Middle Ages

Although it was a poor country riddled with petty kingdoms, Wales was the one region in southern Britain that survived the Anglo-Saxon onslaught following William the Conqueror's victory on the island. The main stay of Wales survival came from its mountainous and wooded terrain, and the very fact that the many rivaling kingdoms within its own borders established a ready-made guerrilla warfare that the royalty of England was ill-prepared to subjugate. Because of the lack of communications once the mountain ridge border was crossed, and the difficulty of sustaining logistics during guerilla ambushes, even William I decided on a defensive posture against the Welsh, wherein he established marches along the border that were charged with preventing Welsh encroachment--by royal rights and authority to build castles, and at the same time he permitted free license to the March lords to advance into Wales.…