Analysis of information sources in references of the Wikipedia article "Siege of Baghdad (1258)" in English language version.
The Georgian and Armenian aristocracy now was bound tightly to the Mongol leading class and the military became of primary importance. The Mongols forced their subjects to participate in their military campaigns. For the local aristocracy, it was sometimes necessary to contribute in order to get some immediate advantages from them. Therefore the intervention of Armenian and Georgian forces in Mongol military operations was not an isolated incident. (...) Around mid-1200, the whole Caucasian region was gripped by Mongol power on one side and the Muslim independent states on the other; the Ismā'īlĭs (Assassins) in the territory between Syria and northern Iran, and the Caliphate of Baghdad. When Hülegü began the military campaign against the caliphate, the Armenian and Georgian aristocracy took the opportunity to eliminate the menace and joined the Mongol armies. The attack on the Assassins' stronghold in Alamūt – which ended with the fall of the city in November 1256 – was planned and executed with the aid of David Lasha. Prince Zak'are, son of Shahanshah, participated in the operations against Baghdad in 1258 and the Armenian aristocracy was fully involved as well. Eastern Christianity embraced the conquest of Baghdad by Hülegü's army as divine revenge. The Mongols massacred the Muslim population of the city but spared the Christians. Hülegü gave the palace of the Dawādār (vice chancellor) to the Nestorian patriarch Makhika. Kirakos describes the fall of Baghdad in joyful terms and states that all the oriental Christians were exulting because after 647 years the "Muslim tyranny" had finally ended.
At the very beginning of 1258 Hülegü and his multi-ethnic armies—including Chinese siege breakers, Armenian and Georgian auxiliaries and quite a few Sunnī Muslim troops from Central Asia, Iran and Iraq— converged on Baghdād from all sides. Fighting began in earnest in mid-January, and the city was taken on February 10, 1258, when the caliph left the city and surrendered to Hülegü.
At the very beginning of 1258 Hülegü and his multi-ethnic armies—including Chinese siege breakers, Armenian and Georgian auxiliaries and quite a few Sunnī Muslim troops from Central Asia, Iran and Iraq— converged on Baghdād from all sides. Fighting began in earnest in mid-January, and the city was taken on February 10, 1258, when the caliph left the city and surrendered to Hülegü.