John of Brienne (brēĕnˈ) [key], c.1170–1237, French crusader. He was a count and in 1210 married Mary, titular queen of Jerusalem. Mary died in 1212, and their daughter, Yolande (1212–28), succeeded to the title under John's regency. John played a conspicuous part in the Fifth Crusade (see Crusades), capturing Damietta in 1219, and in 1222 he went to Europe in search of support. He arranged the marriage (1225) between Yolande and Holy Roman Emperor Frederick II, who promptly claimed the crown of Jerusalem. John, claiming the title for himself, joined with a papal army in invading (1229) Frederick's kingdom in S Italy, while Frederick was absent on crusade. In 1228, John was chosen regent during the minority of Baldwin II, Latin emperor of Constantinople (see Constantinople, Latin Empire of), and he became coemperor in 1231. He successfully defended (1236) Constantinople against the joint forces of Emperor John III of Nicaea and Czar Ivan II of Bulgaria.
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