The society of the Welsh Marches, the sociopolitical and administratively distinct district of the Anglo-Welsh border after the Norman Conquest, was a region constructed from a mosaic of small and larger lordships under the new Norman government after the conquest of 1066. The latter date saw Duke William of Normandy and his followers take over the established state and society of Anglo-Saxon (and Anglo-Scandinavian) England and transform it into a French-speaking and partially ''Frenchified'' ''European'' state, based on the same lines of governance and culture as the new leadership elite''s Continental homeland. This applied to the Anglo-Welsh frontier as it did across England, with the existing higher ranks of society marginalised and mostly replaced - with the irony that the incomers on this border faced a militarily advantageous situation recently created by King Harold''s destruction of the threat of a unified Welsh state under Gruffydd ap Llywelyn ap Seisyll, king of Gwynedd and Powys and conqueror of Deheubarth, in 1063. This precariously reunited state, more of a ''union of crowns'' than a viable long-term regime due to complex Welsh inheritance law and the multitude of potential heirs to the five main Welsh kingdoms, had indeed reconquered parts of western Herefordshire from the English in the 1050s and forced King Edward ''the Confessor'' to recognise this - the Welsh were a serious military threat then and thus caused an English military reaction, which the arriving Normans later followed up. The private army/bodyguard of housecarls that Harold Godwinson relied on to lead his army at the Battle of Hastings, and which the Normans destroyed there, ''blooded'' themselves under Harold (as Earl of Hereford) in fighting off the threat posed by Gruffydd in 1057-63 and had finally broken up his kingdom to install a group of new dynasts as Harold''s nominees. Indeed, the experiment of using ''Norman'' cavalry to defeat the Welsh infantry and castles to defend the landscape had already been tried out in the 1050s, with only limited success - King Edward was half-Norman and used to using French cavalry knights against infantry. But it was William and his new group of frontier lords who reaped the benefit. The post-1066 frontier was governed as a part of the kingdom of England by a military-based ruling class almost entirely North French (mostly but not exclusively Norman) in ethnic origin and cultural orientation, though inter-married with local Anglo-Saxon and Welsh heiresses.

It was not that different in its creation by the first King William from the lands governed by the elite in the rest of his new regime. As with the remainder of England, the pre-1066 ruling class (a mixture of Anglo-Saxon and Scandinavian nobility; in this region, probably mostly ''Anglian'' rather than Saxon or Scandinavian as a part of the old Anglian kingdom of Mercia, not occupied by the Vikings in the late ninth century) were evicted by King William in the years from 1067 and replaced by a more trustworthy group of Normans from his invading army of 1066 and their later reinforcements. Indeed, we have more direct literary evidence than for most of England of the process of removing some native landholders, bringing in Normans who spoke French and formed a militarily coherent body of cavalrymen (able to move around the country faster than and usually defeat the English infantry), and their building a chain of new motte-and-bailey castles as defensive and administrative bases starting in 1067. Resentment at this resulted in a local revolt, led by members of the marginalised pre-1066 elite, headed by Earl Edwin of Mercia (brother-in-law to the late King Harold II) and the legendary guerrilla Eadric the Wild, which was crushed by force with more expropriations following. This resembled the situation across England and the ''Marches'' - the word coming from the word ''Mark'' for ''frontier'', as with the former name of the Anglian kingdom of the midlands, Mercia - was thus not exceptional in origin. In due course the land-hungry and enterprisingly aggressive new warlords on the English side of the (flexible) border moved on into the Welsh kingdoms beyond to seize land and build castles, aided by the constant bickering and sporadic fratricide of the Welsh princes, and land that had been Welsh in linguistic and cultural (and largely ethnic) terms since the stabilisation of the Anglo-Welsh frontier in the eighth century became politically and militarily English. But in ethnic terms the lower ranks of vassals of the (now Anglo-Norman) great lords were decidedly mixed, with the farming lower classes still mainly Welsh, though some blocs of Anglo-Normans - and in Pembrokeshire Flemings - moved into the conquered regions.