This should not have been a surprise. John had rebelled unsuccessfully against Richard's administration while Richard was on the Third Crusade. In the present case, the loss of Richard created an opportunity for Philip II of France to take some of England's possessions on the continent, Évreux and the Vexin. The nobles of Anjou, Maine, and Touraine supported Arthur. John did, however, have the support of Aquitaine and Poitou thanks to his mother, Eleanor of Aquitaine, as well as Normandy. After being declared Duke of Normandy, he sailed to England where he was crowned in Westminster on 27 May.
Although England was largely secure, possessions in France were constantly the target of Philip II. John was forced into treaties with Philip in order to stop the hostilities. The Treaty of Le Goulet in 1200 saw John paying Philip 20,000 marks, giving up lands in Auvergne and Berry, giving up on the areas of Normandy that had been seized by Philip, and giving up his alliance with the Holy Roman Empire, who occasionally was a rival of France. The illustration shows via shades of red the dwindling authority of the Angevins.
John then decided to make a politically advantageous marriage, but there were two problems with that: one is that he was already married, and the second that John's decisions were almost always the wrong ones. Stay tuned.