The Mongol invasion and the alliance against the Mongols
In the fourth and fifth decades of the thirteenth century there appeared from the East the menacing danger of the invasion of the Mongols, namely, the Tartars (in Byzantine sources, "Tahars, Tatars, Atars"). The hordes of Batu (Baty), one of the descendants of the famous Khan Temuchin, who had assumed the title of Jenghiz Khan, i.e., Grand Khan, rushed into present-day European Russia and in their destructive and irresistible onslaught seized Kiev in 1240, then crossed the Carpathians, and arrived at Bohemia before they were forced to retrace their march to the Russian steppes. At the same time the other Mongol group, marching in a more southerly direction, conquered all Armenia with Erzerum and invaded Asia Minor, menacing the Sultanate of Rum or Iconium and the weak Empire of Trebizond. Under the pressure of common danger from the Mongols sprang the alliance of the three states of Asia Minor: the Sultanate of Iconium, the Empire of Nicaea, and the Empire of Trebizond, The Seljuqs and the military forces of Trebizond were defeated by the Mongols. After that, the Sultan of Iconium was compelled to relieve himself by paying tribute and supplying annually horses, hunting dogs, and the like. The Emperor of Trebizond, realizing the impossibility of fighting the Mongols, made a speedy peace with them and, on condition of paying an annual tribute, became a Mongol vassal. Fortunately for the Seljuqs and John Vatatzes, the Mongols occupied themselves with other military enterprises and temporarily suspended their onslaught upon the West, which enabled the Emperor of Nicaea to take decisive measures in the Balkan peninsula.