Even Henry, son of the king of the Romans, commonly called Henry d'Allmaine, though a prince of the blood, joined the party of the barons against the king, the head of his own family Leicester himself, who still resided in France, secretly formed the links of this great conspiracy, and planned the whole scheme of operations.
The princes of Wales, notwithstanding the great power of the monarchs both of the Saxon and Norman line, still preserved authority in their own country.

Though they had often been constrained to pay tribute to the crown of England, they were with difficulty retained in subordination or even in peace; and almost through every reign since the conquest, they had infested the English frontiers with such petty incursions and sudden inroads, as seldom merit to have place in a general history.

The English, still content with repelling their invasions, and chasing them back into their mountains, had never pursued the advantages obtained over them, nor been able, even under their greatest and most active princes, to fix a total, or so much as a feudal subjection on the country.

This advantage was reserved to the present king, the weakest and most indolent.

In the year 1237, Lewellyn, prince of Wales, declining in years and broken with infirmities, but still more harassed with the rebellion and undutiful behavior of his youngest son Griffin, had recourse to the protection of Henry; and consenting to subject his principality, which had so long maintained, or soon recovered, its independence to vassalage under the crown of England, had purchased security and tranquillity on these dishonorable terms.