of the Romans in 800 by the Pope, with this forming the basis for the later Holy Roman Empire. Meanwhile, in Eastern Europe, Krum (795-814) expanded the Bulgarian Empire. The Treaty of Verdun divided Carolingian Empire into West, Middle and East Francia. During the Viking Age (793–1066 AD), Norsemen known as Vikings undertook large-scale raiding, colonizing, conquest, and trading throughout Europe, and reached North America. Voyaging by sea from their homelands in Denmark, Norway and Sweden, the Norse people settled in the British Isles, Ireland, the Faroe Islands, Iceland, Greenland, Normandy, the Baltic coast, and along the Dnieper and Volga trade routes in eastern Europe, where they were also known as Varangians. They also briefly settled in Newfoundland, becoming the first Europeans to reach North America. The Vikings founded several kingdoms and earldoms in Europe: the kingdom of the Isles (Suðreyjar), Orkney (Norðreyjar), York (Jórvík) and the Danelaw (Danalǫg), Dublin (Dyflin), Normandy, and Kievan Rus' (Garðaríki). The Norse homelands were also unified into larger kingdoms during the Viking Age, and the short-lived North Sea Empire included large swathes of Scandinavia and Britain. In 1095, Pope Urban II proclaimed the First Crusade at the Council of Clermont. He encouraged military support for Byzantine Emperor AlexiosI against the Seljuk Turks and an armed pilgrimage to Jerusalem. Across all social strata in western Europe there was an enthusiastic popular response. Volunteers took a public vow to join the crusade. Historians now debate the combination of their motivations, which included the prospect of mass ascension into Heaven at Jerusalem, satisfying feudal obligations, opportunities for renown, and economic and political advantage. Initial successes established four Crusader states in the Near East: the County of Edessa; the Principality of Antioch; the Kingdom of Jerusalem; and the County of Tripoli. The crusader presence remained in the region in some form until the city of Acre fell in 1291, leading to the rapid loss of all remaining territory in the Levant. After this, there were no further crusades to recover the Holy Land. Following the end of the Carolingian Empire, the largest polities in Western Europe were the Holy Roman Empire, the Byzantine Empire, Kingdom of France, and the Kingdom of England. The Catholic Church also wielded tremendous power. In Eastern Europe, the Mongol invasion of Europe killed half the population 1237 to 1241. The resulting power vacuum helped the Teutonic Order, while the Kingdom of Poland and