Despite the momentary respite delivered by Isabella, by the autumn of 1321, the tensions between the two factions of Edward, Isabella and the Despenser, opposing the baronial opposition led by Thomas of Lancaster, were extremely high, with forces still mobilised across the country. At this point, Isabella undertook a pilgrimage to Canterbury, during which she left the traditional route to stop at Leeds Castle in Kent, a fortification held by Bartholomew de Badlesmere, steward of the King's household who had by 1321 joined the ranks of Edward's opponents. Some historians believe that the pilgrimage was a deliberate act by Isabella on Edward's behalf to create a "casus belli". Lord Badlesmere was away at the time, having left his wife Margaret de Clare, Baroness Badlesmere in charge of the castle. When the latter adamantly refused the Queen admittance, fighting broke out outside the castle between Isabella's guards and the garrison, marking the beginning of the Despenser War. Whilst Edward mobilised his own faction and placed Leeds Castle under siege, Isabella was given the Great Seal and assumed control of the royal Chancery from the Tower of London. After surrendering to Edward's forces on 31 October 1321, Margaret, Baroness Badlesmere and her children were sent to the Tower, and 13 of the Leeds garrison were hanged. By January 1322, Edward's army, reinforced by the Despensers returning from exile, had forced the surrender of the Mortimers, and by March Lancaster himself had been captured after the Battle of Boroughbridge; Lancaster was promptly executed, leaving Edward and the Despensers victorious.