On 24 July 840 in Strasbourg, Lothair precipitated a new civil war by declaring his imperium over all the lands of the empire and, joining with his nephew Pepin II of Aquitaine, attacked the Loire Valley. While Ermenaud III of Auxerre, Arnulf of Sens, Audri of Autun, and Gerard II of Paris pledged themselves for Lothair, Guerin and Adalbert of Avallon remained with Charles the Bald.
In Strasbourg on 24 July 840, Lothair sparked a new civil strife by asserting his authority over all the empire's lands and, in conjunction with his nephew Pepin II of Aquitaine, invaded the Loire Valley. Conversely, Ermenaud III of Auxerre, Arnulf of Sens, Audri of Autun, and Gerard II of Paris pledged their support to Lothair, whereas Guerin and Adalbert of Avallon remained faithful to Charles the Bald.