Throughout the fourteenth century English monarchs were at war with a variety of enemies, both from within the British Isles and from the continent. At various times there was a fear that the Scots might take the opportunity to mount cross-border raids or to carry out naval attacks on English ports and ships. Although the danger from Wales after the 1280s has been dismissed by some commentators, contemporary records show that elements of unrest persisted there. Indeed, on many occasions during the fourteenth century, whenever England itself was threatened from without, the Welsh were perceived as a very real potential menace and their loyalties were regarded with suspicion. Most particularly, war with the French and their Genoese and Castilian allies, especially from the 1330s onwards, brought with it the frequent menace of sea-borne attacks on the coasts and on shipping, coupled, on several occasions, with the fears that a full-scale invasion was imminent. Moreover, in the course of the century there were two significant invasions aimed at overthrowing the existing regime, the first by Isabella and Mortimer in 1326, and the second by Henry of Bolingbroke in 1399. Furthermore, English monarchs were also well aware that the risk of potential attack intensified whenever an overseas campaign was in the offing because of the resulting reduction in the numbers of available defenders and the possibility that enemies might mount diversionary or retaliatory assaults on England. It was also difficult to conceal from an enemy preparations for major military ventures abroad. Thus, no large army ever departed from these shores without the crown's first ensuring that measures had been taken for the defence of the realm in its absence.

As part of the precautions against such threats, there was in place a mechanism which provided manpower for the defence of the realm. This system had not been developed in response to the contemporary menace, but, instead, had gradually evolved over the centuries since the Norman Conquest. In the course of the fourteenth century, especially during the wars with France and Scotland, defensive measures underwent experiment and change, as the crown continuously sought to improve their efficiency. The practices were rooted in traditions harking back to the Anglo-Saxon fyrd. These traditions had been modified by statute, experiment and custom during the twelfth and thirteenth centuries.