Two "counties palatine" were created by William I on the newly formed borders of Wales. The "earls" selected were practically independent administrators of the lands they had been awarded. The Palatinate of Chester, and The Palatinate of Shrewsbury were designed by this military mind to oppose the more powerful Welsh kingdoms of Gwynedd and Powys. Chester was over against the Princes of Gwynedd, whose power stretched out from Snowdon to Flint in the northwest. Shrewsbury was over against the Princes of Powys, who where settled on the upper Severn and upper Dee. These "earls palatine" had to hold the border [for William I], and were allowed to conquer across this border as they could.
The first "Earl of Chester" was the nephew of William I, named Hugh of Avranches. The first "Earl of Shrewsbury" was Roger of Montgomery, who had been left in charge of Normandy while William was taking control of Anglo-Saxon England. Personal loyalty was the key. This loyalty was expected to bind them to "the crown" [William I], and keep them from deciding to take matters into their own hands, and rebel against the crown.
Thus, the "Normanisation" of the Welsh borders began. This began as a conscious co-operation under sanction of the king, William I. A Norman colony with its own rights planted at the most important posts along the border of Wales. The beginning of the end!