Formation and borders
In August 843, after three years of civil war following the death of Louis the Pious on 20 June 840, the Treaty of Verdun was signed by his three sons and heirs. The youngest, Charles the Bald, received western Francia. The contemporary West Frankish Annales Bertiniani describes Charles arriving at Verdun, "where the distribution of portions" took place. After describing the portions of his brothers, Lothair the Emperor (Middle Francia) and Louis the German (East Francia), he notes that "the rest as far as Spain they ceded to Charles". The Annales Fuldenses of East Francia describe Charles as holding the western part after the kingdom was "divided in three".
Since the death of King Pippin I of Aquitaine in December 838, his son had been recognised by the Aquitainian nobility as King Pippin II of Aquitaine, although the succession had not been recognised by the emperor. Charles the Bald was at war with Pippin II from the start of his reign in 840, and the Treaty of Verdun ignored the claimant and assigned Aquitaine to Charles. Accordingly, in June 845, after several military defeats, Charles signed the
Treaty of Benoît-sur-Loire and recognised his nephew's rule. This agreement lasted until 25 March 848, when the Aquitainian barons recognised Charles as their king. Thereafter Charles's armies had the upper hand, and by 849 had secured most of Aquitaine. In May, Charles had himself crowned "King of the Franks and Aquitainians" in Orléans. Archbishop Wenilo of Sens officiated at the coronation, which included the first instance of royal unction in West Francia. The idea of anointing Charles may be owed to Archbishop Hincmar of Reims, who composed no less than four ordines describing appropriate liturgies for a royal consecration. By the time of the Synod of Quierzy (858), Hincmar was claiming that Charles was anointed to the entire West Frankish kingdom. With the Treaty of Mersen in 870 the western part of Lotharingia was added to West Francia. In 875 Charles the Bald was crowned Emperor of Rome.
The last record in the Annales Bertiniani dates to 882, and so the only contemporary narrative source for the next eighteen years in West Francia is the Annales Vedastini. The next set of original annals from the West Frankish kingdom are those of Flodoard, who began his account with the year 919.