The Battle of Samara Bend (Монгольско-булгарское сражение), also known as the Battle of Kernek, was the first battle between the Volga Bulgaria and the Mongol Empire, taking place during the autumn of 1223 at the southern border of Volga Bulgaria. It is famous for being the first battle that the Mongol Horde lost. The battle began with the Bulgar forces retreating and the Mongols pursuing them, leading them successfully into a Bulgar ambush. The Bulgars counterattacked the Mongols, and drove them back. The Bulgars were nomadic tribes originally from the Pontic–Caspian steppe just north of the Black Sea. In the mid-7th century, the group split; some migrated westward to Central Europe, forming the First Bulgarian Empire in the Balkans, while others migrated northeastward towards the confluence of the Volga and Kama rivers near modern-day Kazan, founding Volga Bulgaria. The Volga Bulgars converted to Islam after it was declared the official state religion in 922, establishing significant trade between the Islamic world and Europe. Despite peaceful relations with Kievan Rus' during the 10th and 11th centuries, the principality of Vladimir-Suzdal began expanding its territory in the middle Volga region during the 12th century, and subsequent disputes over trade in the region resulted in hostilities with the Volga Bulgars. Various Bulgar towns and villages were conquered by the Kievan Rus', referred to as Brjahimov in old Bulgar. The conquest led the Bulgars to establish a new capital at Bilar (also known as Biljarsk or Biler), and the weakening of the Volga-Bulgar state. On 12 January 1221, Shah Muhammad II of Khwarezm died while retreating from the Mongols on the island of Abeskum during Genghis Khan's destruction of the Khwarezmid Empire. Upon hearing the news of the Shah's death, Genghis Khan summoned his general, Subutai, to Samarkand. Subutai offered him advice on how best to defeat the new Shah, Jalal ad-Din Mingburnu. He requested not to be part of the final campaign, and instead proposed to reconnoiter the west bank of the Caspian Sea and the steppes beyond.