John of Brienne in the context of "Maria of Montferrat"

The Fifth Crusade (September 1217 – August 29, 1221) was a campaign in a series of Crusades by Western Europeans to reacquire Jerusalem and the rest of the Holy Land by first conquering Egypt, ruled by the powerful Ayyubid sultanate, led by al-Adil, brother of Saladin.

After the failure of the Fourth Crusade, Innocent III again called for a crusade, and began organizing Crusading armies led by Andrew II of Hungary and Leopold VI of Austria, soon to be joined by John of Brienne, titular King of Jerusalem. An initial campaign in late 1217 in Syria was inconclusive, and Andrew departed. A German army led by cleric Oliver of Paderborn, and a mixed army of Dutch, Flemish and Frisian soldiers led by William I of Holland, then joined the Crusade in Acre, with a goal of first conquering Egypt, viewed as the key to Jerusalem. There, cardinal Pelagius Galvani arrived as papal legate and de facto leader of the Crusade, supported by John of Brienne and the masters of the Templars, Hospitallers and Teutonic Knights. Holy Roman Emperor Frederick II, who had taken the cross in 1215, did not participate as promised.

Hugh I (French: Hugues; Greek: Ούγος (Oúgos); 1195 – 10 January 1218) was the king of Cyprus from 1205 until his death. He was nine when he succeeded his father, King Aimery, and his brother-in-law Walter of Montbéliard ruled the kingdom as regent. After reaching the age of majority and assuming personal rule in 1210, Hugh fell out with Walter, who fled to the Kingdom of Jerusalem. He reversed Walter's policies, making peace with the Seljuqs of Rum and siding with the Armenians in the War of the Antiochene Succession. Pope Innocent III rebuked him for his hostility to the king of Jerusalem, John of Brienne, and for interfering in church appointments. Hugh embarked on the Fifth Crusade in late 1217, but died of an illness in Tripoli soon after. He was succeeded by his infant son, Henry I.

Isabella II (Old French: Ysabel; 1212 – May 1228), sometimes called Isabella of Brienne and erroneously Yolanda, was the queen of Jerusalem who reigned from 1212 to 1228. She was the daughter and successor of Maria of Montferrat, who died shortly after giving birth to her. Like her mother, Isabella died young before she could make an impression on politics.

Isabella's father, John of Brienne, ruled during her long minority; while he continued to regard himself as king for life, his opponents insisted that he was merely regent for Isabella. In 1223 John arranged for her to marry Emperor Frederick II, king of Sicily. A proxy wedding was held in the Kingdom of Jerusalem in August 1225, followed by Isabella's coronation as queen of Jerusalem. She then promptly departed for the Kingdom of Sicily, where she married Frederick in person. The marriage made her queen of Sicily and empress of the Holy Roman Empire. Defying his agreement with her father, Frederick declared himself king of Jerusalem immediately after their wedding and seized control of her kingdom. He sidelined Isabella, whose role in government was minimal. Her father's supporters alleged that Frederick abused her. She died shortly after giving birth to her only son, Conrad II, who succeeded her under Frederick's tutelage.