This book seeks to explore the role of the Welsh in England's armies and in England's wars between Edward I's conquest of Wales and Henry V's conquest of Normandy. It concerns the structure and composition of armies, the group dynamics within them, and the social networks and hierarchies which underpinned them. What sort of Welshmen became soldiers? How was Welsh society organised for war? What impact did wider political considerations have upon Welsh service in England's armies? War in English service inevitably had a colonial flavour in the years after the conquest of Gwynedd, and war played its part in the process of resettlement. The employment of Welshmen in England's wars in Scotland, Flanders and later, the wars pursuing the English claim to the throne of France, now called the Hundred Years War, played a key part in shaping later medieval Wales.

It has often been stated, and is still widely believed, that the Welsh archer in his ‘knitted Monmouth cap’ was a key part of every English victory in the Hundred Years War. A possible origin may lie in Shakespeare's Henry V (1599). In the play, the garrulous captain Fluellen reminds the king not of the number or importance of Welshmen in his army, but of those in the army of his great-uncle, Edward the Black Prince, at Crécy. It is also an article of faith in some quarters that the longbow was a curiously Welsh weapon whose secret was imparted to the English through Edward I's wars of conquest. This is an assertion that it is difficult for the evidence to sustain, but is nonetheless one of the key elements of Welsh popular history.

What follows is a study in two parts. Part I offers a chronological account of the involvement of Welshmen in English armies between the conquest of Gwynedd in 1282–83 and the end of the reign of Henry V in 1422. In doing so, it considers the continuation of Edward I's attempts to master the British Isles, addressing the wars in Scotland that dominated English military affairs from the 1290s to the 1340s. Edward I's reign also contained wars against France, the first after the conquest of Wales being in Gascony, the second, in the winter of 1297–98, in Flanders.