By the early 9th century AD, large parts of Central Europe had been united under the rule of the Frankish leader Charlemagne, who defeated the Lombards, Saxons and other Germanic peoples and established the Carolingian Empire. Charlemagne was crowned emperor by Pope Leo I in 800. During the rule of Charlemagne's successors, the Carolingian Empire descended into civil war. The empire was eventually partioned at the Treaty of Verdun (843), resulting in the creation of the states of West Francia, Middle Francia and East Francia (led by Louis the German). Beginning with Henry the Fowler, Saxon dynasties dominated the German lands, and under his son Otto I, Middle Francia and East Francia, which were mostly German, became part of the Kingdom of Germany, which constituted the core of the Holy Roman Empire. Leaders of tribal duchies such as Bavaria, Franconia, Swabia, Saxony and Lorraine continued to wield considerable power independent of the king. German kings were elected by members of the noble families, who often sought have weak kings elected in order to preserve their own independence. This prevented an early unification of the Germans and contributed to the formation of strong German national groups, such as the Bavarians, Swabians and Franconians.