Lothair I
When the emperor Louis died in 840, and Lothair I claimed the whole Empire, Louis allied with Charles the Bald, and defeated Lothair I and their nephew Pepin II of Aquitaine, son of Pepin I of Aquitaine, at the Battle of Fontenoy in June 841. Both sides suffered heavy casualties. According to the Annals of Fulda, it was the biggest bloodbath the Franks had experienced since time immemorial. At the same time, it was Louis's last battle in the struggle for the unification of the kingdom.