a busy period devoted to royal service. In 1437, possibly because of Gloucester's patronage, Mowbray was appointed Warden of the Eastern March for a one-year term. He had little experience of the north of England, yet was paid wartime wages of £5,000 to campaign against the Scots. Mowbray returned to Calais and Guînes in 1438, leading an expedition to strengthen their defences as Burgundy still presented a threat. Although he shortly after returned to England, in June 1439 he was again back in Calais, at Oye, escorting Archbishop John Kemp's diplomatic mission to the peace conference. Possibly Mowbray disapproved of royal foreign policy, which was then aimed at making peace with the French. Feud with William de la Pole For much of the 1430s, Mowbray had problems in East Anglia, where the bulk of his estates now lay. William de la Pole become increasingly powerful, both at court and in the region, and was Mowbray's biggest rival. Mowbray had enough political clout in the 1430s to control parliamentary representation in Suffolk, but the local importance of the duke weakened his grasp. Mowbray clashed with de la Pole, and committed many illegalities doing so. These included damaging property of rivals, assaults, false allegations of outlawry (with confiscation of goods), and even murder. For Mowbray, East Anglia as the focus of his landed authority was forced upon him since this was where the majority of his estates were located: much of his Lincolnshire inheritance was held by his mother as dower. He was then a newcomer to political society in the region, and had to share influence with others. By the time of his majority, de la Pole—with his links to central government and the King—was an established power in the region. He hindered Mowbray's attempts at regional domination for over a decade, leading to a feud that stretched from the moment Mowbray became Duke of Norfolk to the murder of de la Pole in 1450. The feud was often violent, and lead to fighting between their followers. In 1435, Robert Wingfield, Mowbray's steward of Framlingham, led a group of Mowbray retainers who murdered James Andrew, one of de la Pole's men. When local aldermen attempted to arrest Wingfield's party, the latter rained arrow fire upon the aldermen, but Mowbray secured royal pardons for those responsible. By 1440, de la Pole was a royal favourite. He instigated Mowbray's imprisonment on at least