In medieval history, West Francia (Medieval Latin: ) or the Kingdom of the West Franks () refers to the western part of the Frankish Empire established by Charlemagne. It was the forerunner of the future Kingdom of France and existed from 843 to 987. West Francia emerged from the partition of the Carolingian Empire in 843 under the Treaty of Verdun following the death of Charlemagne's son, Louis the Pious. It is considered the first separate polity in French history. West Francia extended further north and south than modern metropolitan France, but it did not extend as far east. It did not include such future French holdings as Lorraine, the County and Kingdom of Burgundy (the duchy was already a part of West Francia), Alsace and Provence in the east and southeast for example. It also did not include the Brittany peninsula in the west. In addition, by the 10th century the authority of the West Frankish monarchs was greatly reduced. This was contrasted by the evergrowing power of their vassals over their large and usually territorially contiguous fiefs. The power vacuum left by a weak royal authority meant wars between fiefs were rampant, and so were conflicts between the vassals and the Frankish monarchs themselves. The period was also marked by endless Viking raids on the kingdom and clashes between the West Franks and the Norsemen. This eventually led to the establishment of the Duchy of Normandy, which was granted to the Norseman Rollo and his men following their unsuccessful siege at Chartres in 911 in exchange for an oath of fealty to King Charles the Simple. The fiefdom of Normandy was first a county then a duchy, and like other great fiefs of West Francia became largely autonomous, with magnates even more powerful than their monarch. In Brittany and Catalonia the authority of the West Frankish king was barely felt. West Frankish kings were elected by the secular and ecclesiastic magnates, and for the half-century between 888 and 936 candidates from the Carolingian and Robertian houses were alternately chosen as monarchs. By this time the power of king became weaker and more nominal, as the regional dukes and nobles became more powerful in their semi-independent regions. The Robertians, after becoming counts of Paris and dukes of France, became kings themselves and established the Capetian dynasty after 987, which is, although arbitrary, generally defined as the gradual transition towards