How did Louis I’s conflicts with his sons lead to civil war after his death?

Louis I’s attempts to revise the succession plans for his empire created deep-seated familial and political divisions that erupted into civil war following his death in 840.12

Initially, Louis sought to maintain imperial unity through the Ordinatio imperii of 817, which designated his eldest son, Lothar I, as sole heir while granting his younger sons, Pippin and Louis the German, subordinate kingdoms. However, the birth of a fourth son, Charles II (the Bald), to Louis’s second wife, Judith, led the emperor to repeatedly reallocate territory to accommodate Charles.13425

These revisions alienated the older sons, who viewed the changes as a threat to their inheritance and status. After Louis I died, these unresolved tensions triggered open warfare. Lothar I attempted to assert his rights as sole heir under the original 817 decree, but he was opposed by his brothers, Louis the German and Charles the Bald. Their conflict culminated in the Battle of Fontenoy (841) and was eventually settled by the Treaty of Verdun in 843, which partitioned the empire and marked the beginning of its dissolution.23