The English conquest of Wales was largely driven by the actions of the Marcher lords, those who held lands along the English-Welsh border. These were some of the most powerful subjects of the Kings of England at any time. They had far more independence than the majority of the barons with legal powers "like unto a king". These powers are summaried in the Wikipedia article. One point I would disagree with is the opening staement that they were 'trusted'. That was the theory but in practice their power meant that they had to be carefully handled by the king.
At the time of the 2nd Barons' War, the three Marcher Earls were those of Hereford, Pembroke and Gloucester. The Earldom of Shrewsbury had become extinct and the Earldom of Chester was held by Prince Edward. Another earldom, that of March, was created under Edward I and first held by Roger Mortimer.
I've already mentioned Hereford and Pembroke, so here is Gilbert de Clare, Earl of Gloucester and of Hertford. 'Red' Gilbert (probably on account of his hair) had inherited the earldom at an early age - he wasn't actually knighted until de Montfort did so just before the Battle of Lewes. He threw in his lot with the Barons despite being married to the king's neice who was also daughter of the Earl of Pembroke. His actions probably led to their estrangement so that they were legally separated after the war.
He led the central division of the Baronial army at Lewes. However, he fell out with de Montfort and began to aid the royalist party, joining Edward for Kenilworth and Evesham. He reaped the rewards, being given further lands in Wales. He had various disagreements with Llewellyn and led Edward's southern forces against the Welsh though without success.
He even engaged in a private war with de Bohun, Earl of Hereford. This was within the rights of a Marcher Lord but Edward stamped on it, prosecuting both parties and briefly imprisoning them to make the point.
One feature of Marcher warfare were the muntatores, the light cavalry known to have been used in Staffordshire and Shropshire from the late 11th century. They are described as having hauberk, iron helmet and lance. The lack of any mention of shields may not be significant - they are also not mentioned for the infantry the Assizes of arms and it is generally assumed that the infantry had them so the muntatores may also have done so. This article describes them and proposes a link between them and the hobelars which are often thought to have originated in Ireland.
There may not have been any noticeable difference between the muntatores and the lesser equipped part of the Welsh cavalry. For my muntatores I have simply used some of the Legio Heroica sergeeants, mostly with no leg armour, on unbarded horses. However, for my Welsh cavalry I have used some Outpost cavalry and these may also be suitable for muntatores. Outpost's later sergeants are also suitable - they have kettle hats and cerveillieres. I don't have any comparison photos for Outpost yet but I would judge them pretty compatible with Mirliton and similar.
The English conquest of Wales relied to some extent on the fractious nature of Welsh politics. The Marcher lords and the King often involved themselves in a dispute between two Welsh parties and came away with gains from the loser. Some other gains were made through marriage and others through blatant annexation.
The Welsh also involved themselves in English politics - much of de Montfort's army at Evesham was composed of Welsh infantry and Llewellyn 'the last' was married to de Montfort's daughter.
By the mid-13th century, most of the south of Wales was under Marcher control and this seems to be the main area where archery was dominant.The north seems to have been fonder of spearmen and there were various occasions where they stood up to and defeated English knights, though often with the aid of favourable terrain.
The dress of these spearman is somewhat debateable.There is evidence that the standard form of dress found over most of Western Europe was becoming normal but there is other evidence that a more distinctive mode of dress remained in use. This has been dismissed as being English writers dismissing a more barbarous style of dress but the description seems no more outlandish or unsuitable than the broadly similar clothing worn in the Scottish highlands i.e. linen shirt and woolen cloak. Note - I don't think the overall appearance of these two forms of dress would have been similar, just the components. This article summarises the evidence. You can find Giraldus Cambrienensis' 12th century description here and some later depictions of Welsh soldiers here. This is one of the pictures from the National Archives of Wales.
There is a Flemish description which seems to confirm the appearance of the Welsh at the end of the 13th century. The Flemish version of van Velthem's Spiegel Historiael is here - the relevant section is around line 90. The link above has a translation into English.
One thing which I've pondered is the translation of 'roden rocke'. These are the red tunics which are mentioned in various books. I have absolutely no evidence for this, but I wonder if there is a Medieval Flemish equivalent of 'rude' (from the latin 'rudis') which this could represent. 'Rude garment' is a phrase which crops up in English to mean a simple or rough piece of clothing often used for something like St Francis's garb. The usual explanation however is that the king donated red cloth to them as an early form of livery. I have painted up some of my Welsh spearmen in red and the remainder in a motley collection using colours in the laws of Hywel Dda and here.
These are some of my Welsh spearmen.
From left to right they are from Lancashire, Donnington, Khurasan, Donnington, Khurasan and Lancashire.
Overall, my favourites are the Donnington figures. They have a proper hood and the proportions are IMHO the best. as can be seen, the three makes are very compatible in size. These are the first Lancashire figures I've used for a while and was largely as a result of them putting photos on their website. There is a third pose which I haven't used - it may well paint up well enough but I didn't like the figures as much. For the price it is affordable to discard the odd figure! Incidentally, their English foot such as these spearmen are very good figures - despite the number of feudal infantry I already have I shall have to find a home for them. I shall also probably use their Welsh archers as I seem to have accidentally found myself in possession of most of a Welsh army! I already have a few as samples but haven't painted them. They have a lot more action in the pose than Essex's Welsh.