In the 1220s and 1230s Mongol hordes appeared on the scene. Having conquered the north-eastern part of China (1211-1215), the Mongol leader Genghiz-Khan marched out against Central Asia, launching an offensive on Muhammad, Shah of Khwarazm (1200-1220).See The detachment of the Mongol army, led by Djebb and Subudai, the same detachment, that had made war on Muhammad and his son Jalal-ad-Din (1200-1231), attacked Georgia several times in the early 1220s. In 1222 the Georgians suffered defeat. Mongol invasions resumed in 1235. Prior to that Jalal-ad-Din, pursued by the Mongols, attacked Georgia. The Georgians lost the battle of Garnisi.(60,000 Georgian against 200,000 the Khwarazmians) The royal court with Queen Rusudan (1223-1245) moved to Kutaisi. A year later Jalal-ad-Din took Tbilisi. The people fought courageously, the city passing from hand to hand. In 1227-1228 Jalal-ad-Din attacked Georgia again. According to the chronicler, over 100 thousand lost their lives when the city fell to the Khwarazmians for the first time. They were compelled to change religion and become Muslims, but no one did it and thus almost the whole population of Tbilisi was assassinated.
From the magnificent History of Georgia by Academician R. Metreveli, Tbilisi State University, see the whole article here