Al-Musta'sim

Abu Ahmad Abdallah ibn al-Mustansir bi'llah (Arabic: أبو أحمد عبد الله بن المستنصر بالله), better known by his regnal title Al-Mustaʿṣim bi-llāh (Arabic: المستعصم بالله;‎ 1213 – 20 February 1258), was the 37th and last caliph from the Abbasid dynasty ruling from Baghdad. He held the title from 1242 until his death in 1258.

Abu Ahmad Abdallah (future caliph Al-Musta'sim) was a son of the Abbasid caliph al-Mustansir, and his mother was Hajir. He was born in 1213. After the death of his father, al-Musta'sim succeeded to the throne in late 1242.

He is noted for his opposition to the rise of Shajar al-Durr to the Egyptian throne during the Seventh Crusade. He sent a message from Baghdad to the Mamluks in Egypt that said: "If you do not have men there tell us so we can send you men." However, al-Musta'sim had to face the greatest menace against the caliphate since its establishment in 632: the invasion of the Mongol forces that, under Hulagu Khan, had already wiped out any resistance in Transoxiana and Khorasan. Shortly thereafter, in 1255-1256, Hulagu Khan forced the Abbasid Caliphate to lend him their forces for his campaign against the Alamut region in modern-day Iran.

News of the murder of al-Muazzam Turanshah and the inauguration of Shajar al-Durr as the new sultan reached Syria. The Syrian emirs were asked to pay homage to Shajar al-Durr but they refused and the Sultan's deputy in Al Karak rebelled against Cairo. The Syrian emirs in Damascus gave the city to an-Nasir Yusuf, the Ayyubid emir of Aleppo, and the Mamluks in Cairo responded by arresting the emirs who were loyal to the Ayyubids in Egypt. In addition to the Ayyubids in Syria, the Abbasid caliph al-Musta'sim in Baghdad also rejected the Mamluk move in Egypt and refused to recognize Shajar al-Dur as a sultan. The refusal of the Caliph to recognize Shajar al-Durr as the new sultan was a great setback to the Mamluks in Egypt, as the custom during the Ayyubid era was that the Sultan could gain legitimacy only through the recognition of the Abbasid caliph. The Mamluks, therefore, decided to install Izz al-Din Aybak as a new sultan. He married Shajar al-Durr, who abdicated and passed the throne to him after she had ruled Egypt as sultan for about three months. Though the period of Shajar al-Durr's rule as a sultan was of short duration, it witnessed two important events in history: the expelling of Louis IX from Egypt, which marked the end of the Crusaders' ambition to conquer the southern Mediterranean basin; and the death of the Ayyubid dynasty and the birth of the Mamluk state which would dominate the southern Mediterranean for decades.

To please the Caliph and secure his recognition, Aybak announced that he was merely a representative of the Abbasid caliph in Baghdad. To placate the Ayyubids in Syria, the Mamluks nominated an Ayyubid child named al-Sharaf Musa as a co-sultan. But this did not satisfy the Ayyubids, and armed conflict between the Mamluks and the Ayyubids broke out. The Caliph in Baghdad, preoccupied with the Mongols who were raiding territories not far from his capital, preferred to see the matter settled peacefully between the Mamluks and the Ayyubids. Through the negotiation and mediation of the Caliph that followed the bloody conflict, the militarily superior Mamluks reached an agreement with the Ayyubids that gave them control over southern Palestine, including Gaza, Jerusalem and the Syrian coast. By this agreement, the Mamluks not only added new territories but also gained recognition for their rule.

In 1258, Hulagu invaded the Abbasid domain, which then consisted of only Baghdad, its immediate surroundings, and southern Iraq. In his campaign to conquer Baghdad, Hulagu Khan had several columns advance simultaneously on the city, and laid siege to it. The Mongols kept the people of Abbasid Caliphate in their capital and executed those who tried to flee.

Baghdad was sacked on 10 February and the caliph was killed by Hulagu Khan soon afterward. It is reckoned that the Mongols did not want to shed "royal blood", so they wrapped him in a rug and trampled him to death with their horses. Some of his sons were massacred as well. The surviving son, Abu'l-Abbas Ahmad, was sent as a prisoner to Mongolia, where Mongolian historians report he married and fathered children, a daughter Aisha and a son Rukn al-Din Ahmad who had descendants, but played no role in Islam thereafter.

The Travels of Marco Polo reports that upon finding the caliph's great stores of treasure which could have been spent on the defense of his realm, Hulagu Khan locked him in his treasure room without food or water, telling him "eat of thy treasure as much as thou wilt, since thou art so fond of it."