When the Frankish kingdom was divided by the Treaty of Verdun (843) the territory east of the Rhine became the East Frankish Kingdom, from which the present Germany has developed. A strong central authority was lacking during the reigns of the weak East Frankish kings of the Carolingian dynasty. Each German tribe was forced to rely upon itself for defence against the incursions of the Norsemen from the north and of the Slavs from the east, consequently the tribes once more chose dukes as rulers.