What did the Treaty of Mersen accomplish?

The Treaty of Mersen, concluded in 870 AD, played a crucial role in the ongoing efforts to stabilize and delineate territories within the Frankish kingdom following the fragmentation of the Carolingian Empire. Specifically, this treaty reaffirmed and formalized the borders that had been established by the earlier Treaty of Verdun in 843. The Treaty of Verdun had divided the empire among the grandsons of Charlemagne into three separate kingdoms, and the Treaty of Mersen further clarified and organized these divisions as they were being contested and altered over the years.

By dealing with the ongoing disputes and tensions among the leaders of these fragmented territories, Mersen created a more definitive framework for the boundaries between the realms of Charles the Bald and Louis the German, thereby securing a more structured partition of the territories, which would be significant in shaping future European political landscapes. This focus on formalizing established borders highlights the importance of treaties in managing power dynamics and territorial claims in the post-Carolingian era.