Margaret of Provence sibling Beatrice of Provence
During the Seventh Crusade
Margaret accompanied Louis on the Seventh Crusade (their first). Her sister Beatrice also joined. Though initially the crusade met with some success, such as the capture of Damietta in 1249, it became a disaster after the king's brother was killed and the king then captured.
Queen Margaret was responsible for negotiations and gathering enough silver for his ransom. She was thus for a brief time the only woman ever to lead a crusade. In 1250, while in Damietta, where she earlier in the same year successfully maintained order, she gave birth to John Tristan.The chronicler Jean de Joinville, who was not a priest, reports incidents demonstrating Margaret's bravery after Louis was made prisoner in Egypt. For example, she decisively acted to assure a food supply for the Christians in Damietta and went so far as to ask the knight who guarded her bedchamber to kill her and her newborn son if the city should fall to the Arabs. She also convinced some of those who had been about to leave to remain in Damietta and defend it. Joinville also recounts incidents that demonstrate Margaret's good humor, as on one occasion when Joinville sent her some fine cloth and, when the queen saw his messenger arrive carrying them, she mistakenly knelt down thinking that he  was bringing her holy relics.  When she realized her mistake, she burst into laughter and ordered the messenger, "Tell your master evil days await him, for he has made me kneel to his camelines!"
However, Joinville also remarked with noticeable disapproval that Louis rarely asked after his wife and children. In a moment of extreme danger during a terrible storm on the sea voyage back to France from the Crusade, Margaret begged Joinville to do something to help; he told her to pray for deliverance and to vow that when they reached France she would go on a pilgrimage and offer a golden ship with images of the king, herself and her children in thanks for their escape from the storm.  Margaret could only reply that she dared not make such a vow without the king's permission, because when he discovered that she had done so, he would never let her make the pilgrimage.  In the end, Joinville promised her that if she made the vow he would make the pilgrimage for her, and when they reached France he did so.Political significance
Her leadership during the crusade had brought her international prestige and after she returned to France, Margaret was often asked to mediate disputes. She feared the ambitions of her brother-in-law Charles, though, and strengthened the bond with her sister Eleanor and Eleanor's husband, King Henry III of England, as a counterweight. In 1254, she and her husband invited them to spend Christmas in Paris.
Then, in 1259, the Treaty of Paris was concluded after the relationship between Louis and Henry had improved. Margaret was present during the negotiations along with all of her sisters and her mother.
In later years, Louis became vexed with Margaret's ambition.  It seems that when it came to politics or diplomacy she was indeed ambitious, but somewhat inept.  An English envoy at Paris in the 1250s reported to the English court, evidently in some disgust, that "the queen of France is tedious in word and deed," and it is clear from the envoy's report that he was not impressed with her efforts to create an opportunity for herself to engage in affairs of state.  After the death of her eldest son Louis in 1260, Margaret induced the next son, Philip, to swear an oath that no matter at what age he succeeded to the throne, he would remain under her tutelage until the age of thirty.  When Louis found out about the oath, he immediately asked the pope to excuse Philip from the vow on the grounds that he himself had not authorized it, and the pope immediately obliged. This ended Margaret's attempt to make herself a second Blanche of Castile.  Margaret subsequently failed as well to influence her nephew King Edward I of England to avoid a marriage project for one of his daughters that would promote the interests in her native Provence of her brother-in-law, Charles of Anjou, who had married her youngest sister Beatrice.
brother or sister kin