It is alleged by some that the duke of Brunswick was well-inclined to enter into the views of the
pope, but that he found he could neither raise men nor money sufficient to warrant even a probability of success. This is doubtful, for had Otto been ambitious, he might have obtained the empire without much difficulty; and supported as he was by
England and
Denmark, it is not likely that he could have been at a loss for an army, or for the means of supporting it. As a proof that Otto had the full confidence and support of the
king of England, at the moment he obtained his liberty, he wrote to communicate the same to
Henry III, who was his cousin, and as Henry's answer dated 6 March 1229 has been preserved by
Thomas Rymer, it becomes a valuable part of these annals, as it puts conjecture beyond a doubt. Later Henry send a letter to the Pope, in which he repeats his thanks to
Pope Gregory IX for the zealous part he had taken in procuring the freedom of his dear cousin the duke of Brunswick, and adds, "that as Christian Princes may approach his Holiness with their petitions, he ventures to supplicate a continuance of his especial favor to his said cousin, which by reason of their near connexion in blood he would esteem as much as if shewn to himself." He implores Gregory to promote Otto's honor whenever it is in his power, and to recommend him to the princes of the empire, as often as he had an opportunity, adding, " that he most firmly believed and trusted in the Lord, that among all the princes of the empire he would be found the one most devoted to the interests of the church; and that as he considered his release from prison owing in a great measure to the influence of the
Apostolic See, he would consequently be the more obsequious to that power. In 1235, Otto achieved an agreement with Emperor Frederick II that ended the dispute between Frederick's
House of Hohenstaufen and the
House of Welf, to which Otto belonged. This dispute had culminated when Henry the Lion was stripped of his duchies in 1180 by Frederick's grandfather,
Frederick Barbarossa. According to this agreement, Otto transferred all of his private property to the emperor, who immediately returned it to him as a hereditary imperial
fief. In this way, Otto reacquired the status of a
prince of the
Holy Roman Empire that Henry the Lion had lost. However, the
Duchy of Saxony, which Henry had held, had since then passed on to
Ascanian dukes, so that the emperor had to create a new duchy for Otto. This was the Duchy of
Brunswick-Lüneburg, named after the two central cities around which Otto's former properties were located. Otto could substantially increase his territory by supporting King
William, who married his daughter
Elisabeth in January 1252. ==Later life and death==