Later, Edmund accompanied his elder brother Edward on his crusade in the Holy Land, where his epithet "Crouchback" originated from a corruption of 'cross back', referring to him wearing a stitched cross on his garments.

[11] Prospects turned grim when Pope Alexander IV succeeded Innocent and faced military pressure from the Holy Roman Empire.

[26] Power in England swung back and forth between Henry and the barons,[27] culminating in the Treaty of Kingston, under which disputes were to be resolved by Edmund's uncles, Richard of Cornwall and King Louis IX of France.

[28][29] Despite the treaty, an open civil war erupted between the royal government and the radical barons led by Simon in the summer of 1263, prompting Edmund to flee from the Tower of London to Dover Castle.

[33] The Second Barons' War finally erupted in April 1264 when Henry's army occupied Simon's territories in the Midlands and advanced to reoccupy a route to France in the southeast.

[34] Accompanied by his mother, Eleanor, Edmund went to France, where he helped to raise a mercenary army, with financial assistance from his uncle Louis, to support his father.

[38][39] Following the Baronial defeat at Evesham on 4 August 1265, Simon was killed and dismembered by the royal army, and his lands and title as Earl of Leicester were forfeited.

On 26 October 1265, Edmund became the Earl of Leicester when his father, King Henry III of England, granted him the title and associated lands, following the re-creation of the earldom.

[26] On 6 December of the same year, Edmund gained control of the castles of Cardigan and Carmarthen, and on 8 January 1266, he acquired the demesnes of Dilwyn, Lugwardine, Marden, Minsterworth and Rodley.

[41]On 28 June of the same year, Edmund acquired the forfeited estates of Robert de Ferrers, 6th Earl of Derby, whose family had held a significant feudatory since the time of Stephen, King of England.

[47] Edmund continued his diplomatic activities by attending the knighting ceremony of his cousin Philip, conducted by his uncle King Louis IX of France, in Paris on 4 June.

Although he had been disappointed by losing the Sicilian crown to his uncle Charles I of Anjou, he had now received a powerful earldom that established the Lancastrian branch of the Plantagenet dynasty.

[61] In an elaborate ceremony on 24 June 1268, Edmund pledged himself to undertake a crusade alongside his elder brother Edward and their cousin Henry of Almain.

[54][61] However, Edmund wanted to ensure the security of his inheritance and decided to marry Isabel's daughter, Aveline de Forz, Countess of Aumale.

Upon the advice of his councilors, Henry chose to remain in England, while Edward led the first group of English crusaders, setting sail from Dover on 20 August that year.

[80] However, Roger Mortimer, 4th Earl of March, presented evidence countering these claims, stating that the chronicles described Edmund as a handsome knight who was skilled in combat.

[58] However, the chronicler John of Trokelowe reported that Edmund and Blanche had also known of each others' reputations as a chivalrous knight and a skilled and beautiful regent, respectively, and they became mutually attracted to each other.

[89][92][93] Blanche's brother Robert II, Count of Artois, an ally to Charles, was furious upon hearing about their engagement, believing the English to still be hostile to France.

[98][99] In early 1277, Edmund was summoned to return to England by Edward, along with other English nobles, to proceed against the Prince of Wales, Llywelyn ap Gruffudd.

[99] Payne had previously had success in the valley of the River Towy, capturing the castles of Dryslywn, Dinefwr, Carreg Cennan and Llandovery, allowing Edmund, who assumed his command, to push further north, seizing the lands of the Welsh noble Rhys ab Maelgwyn and taking Aberystwyth at the end of July 1277.

[104] Since Alphonse died without issue, according to the Treaty of Abbeville of 1259 signed between England and France, the counties as part of Joan's dowry were to be returned to the English crown.

Edmund and the Grand Butler of France John II of Brienne marched to Provins with an army, and the leaders of the mob fled, leaving the gates open.

Edmund and John forfeited the town's privileges and authorities, disarmed the inhabitants of Provins and condemned the leaders of the mob to death or banishment, with Gilbert being excommunicated.

[106] Edmund returned to France and pardoned the town of Provins in July 1281 through the meditation of several church officials and Gilles de Brion, the grand mayor of Donnemarie and brother of Pope Martin IV.

[116][117][118] In addition, Philip relinquished any claim to half of the property acquired and held jointly by Blanche and her first husband King Henry I of Navarre in Champagne, and extended this renouncement to Edmund.

[120] For the rest of the 1280s, Edmund oversaw the affairs of his lands, such as hiring a chaplain for Tutbury Castle, but also accompanied his brother King Edward I of England when he stayed in Gascony for almost three years.

During the assembly at Norham on 13 June 1291 to select the next King of Scotland, Edmund witnessed the submission of rival claims to the Scottish crown under Edward's arbitration.

[123] On 5 February 1292, Edmund was chosen as part of a five-member commission with full authority to establish and enforce regulations to uphold the use of arms in the kingdom.

[133][136] Philip reassured them that they should not be alarmed, as he planned to give a negative answer in public because he did not want to refuse some of his council members who opposed restoring Gascony to English control.

[136] Finally, on 21 April, in a parlement session overseen by Philip, Edward was cited again to appear in Paris with no safe conduct granted nor delay allowed.