When Richard died, John did not gain immediate universal recognition as king. Some regarded his young
nephew, Arthur of Brittany, the son of John's late brother Geoffrey, as the rightful heir. Arthur fought his uncle for the throne, with the support of King
Philip II of France. The conflict between Arthur and King John had fatal consequences. By the May 1200
Treaty of Le Goulet, Philip recognised John over Arthur and the two came to terms regarding John's vassalage for Normandy and the Angevin territories. However, the peace was ephemeral.
The war upset the barons of
Poitou enough for them to seek redress from the King of France, who was King John's
feudal overlord with respect to certain territories on the Continent. In 1202, John was summoned to the French court to answer the charges one of which was his marriage to Isobel of Angouleme who was already engaged to Guy de Lusignan. John was called to Phillip's court after the Lusignans pleaded for his help. John refused and, under feudal law, because of his failure of service to his lord, the French King claimed the lands and territories ruled by King John as Count of Poitou, declaring all John's French territories except
Gascony in the southwest forfeit. The French promptly invaded Normandy; King Philip II invested Arthur with all those fiefs King John once held (except for Normandy), and betrothed him to his daughter Marie.
Needing to supply a war across the Channel, in 1203 John ordered all shipyards (including inland places such as
Gloucester) in England to provide at least one ship, with places such as the newly-built
Portsmouth being responsible for several. He made Portsmouth the new home of the navy (the
Anglo-Saxon kings, such as
Edward the Confessor, had royal harbours at
Sandwich, Kent)and most importantly Hastings. By the end of 1204, he had 45 large galleys available to him, and from then on an average of four new ones every year. He also created an
Admiralty of four admirals, responsible for various parts of the new navy. During John's reign, major improvements were made in ship design, including the addition of sails and removable forecastles. He also created the first big transport ships, called buisses. John is sometimes credited with the founding of the modern
Royal Navy. What is known about this navy comes from the
Pipe Rolls, as these achievements are completely ignored by the chroniclers and early historians.
In the hope of avoiding trouble in England and Wales while he was away fighting to recover his
French lands, in 1205, John formed an alliance by marrying off his illegitimate daughter,
Joan, to the
Welsh prince
Llywelyn the Great.
As part of the war, Arthur attempted to
kidnap his own grandmother, Eleanor of Aquitaine, at Mirebeau, but was defeated and captured by John's forces. Arthur was imprisoned first at Falaise and then at Rouen. No one is certain what happened to Arthur after that. According to the
Margam Annals, on
3 April 1203:
:After King John had captured Arthur and kept him alive in prison for some time in the castle of Rouen... when [John] was drunk he slew [Arthur] with his own hand and tying a heavy stone to the body cast it into the Seine.
However,
Hubert de Burgh, the officer commanding the Rouen fortress, claimed to have delivered Arthur around
Easter 1203 to agents of the King sent to
castrate him and that Arthur had died of
shock. Hubert later retracted his statement and claimed Arthur still lived, but no one ever saw Arthur alive again and the supposition that he was murdered caused Brittany, and later Normandy, to rebel against King John.
Besides Arthur, John also captured his niece,
Eleanor, Fair Maid of Brittany. Eleanor remained a prisoner the rest of her life (which ended in 1241); through deeds such as these, John acquired a reputation for ruthlessness.