Russian troops are defeated by forces of the Blue Horde Khan Arapsha in the Battle on Pyana River.

The Blue Horde was a crucial component of the Mongol Empire established after Genghis Khan's demise in 1227. Functioning as the eastern part of the split Golden Horde, it contrasted with the White Horde's western segment, adhering to the Mongolian and Turkic tradition of cardinal direction colors.

Khan is a historic Turkic and Mongolic title originating among nomadic tribes in the Central and Eastern Eurasian Steppe to refer to a king. It first appears among the Rouran and then the Göktürks as a variant of khagan and implied a subordinate ruler. In the Seljük Empire, it was the highest noble title, ranking above malik (king) and emir (prince). In the Mongol Empire it signified the ruler of a horde (ulus), while the ruler of all the Mongols was the khagan or great khan. It is a title commonly used to signify the head of a Pashtun tribe or clan.

The Battle on Pyana River took place on August 2, 1377 on the Pyana River between the Golden Horde under Arab Shah (Arapsha) and an alliance of Russian principalities led by Prince Ivan Dmitriyevich, made up of the Pereyaslavl, Yaroslavl, Yuryev, Nizhny Novgorod, and Murom principalities.