John was on intimate terms with his nephew, Otho IV., Emperor of Germany and the foe of Philip Augustus, who had supported against him Frederick II., his rival for the empire.

They prepared in concert for a grand attack upon the King of France, and they had won over to their coalition some of his most important vassals, amongst others, Renaud de Dampierre, Count of Boulogne.

Philip determined to divert their attack, whilst anticipating it, by an unexpected enterprise--the invasion of England itself.
Circumstances seemed favorable.

King John, by his oppression and his perfidy, had drawn upon him the hatred and contempt of his people; and the barons of England, supported and guided by the Archbishop of Canterbury, Stephen Langton, had commenced against him the struggle which was to be ended some years afterwards by the forced concession of Magna Charta, that foundation-stone of English liberties.

John, having been embroiled for five years past with the court of Rome, affected to defy the excommunication which the pope had hurled at him, and of which the King of France had been asked by several prelates of the English Church to insure the efficient working.