How did King John become king after Richard I died?

Following the death of Richard I in April 1199, John ascended to the throne primarily because the doctrine of representative succession—which would have favored his nephew, Arthur I—was not yet generally accepted.1

Although Richard had previously recognized Arthur as his heir presumptive, he later disinherited the boy in favor of John after Arthur was reared in the household of Philip II of France. Following Richard's sudden death, John was accepted as king in England and Normandy and was crowned in May 1199.21

John’s accession was supported by his mother, Eleanor of Aquitaine, who actively worked to secure his inheritance against the rival claims of Arthur, who was backed by the French king. While Arthur was initially recognized as successor in Anjou and Maine, John eventually secured recognition of his rights to all of Richard’s French possessions a year later through the Treaty of Le Goulet.231