843 · Verdun, France
Treaty of Verdun Splits the Carolingian Empire
In 843, Charlemagne's three grandsons divided his empire into three kingdoms, ending the dream of a unified Christian Europe and setting the political boundaries that would eventually become France, Germany, and the lands between.
Charlemagne had built something that looked, briefly, like the restoration of the Western Roman Empire — a vast Christian kingdom stretching from the Pyrenees to the Elbe, held together by his personal authority and blessed by the pope. His son Louis the Pious managed to hold it together, barely. But when Louis died in 840, his three sons went to war over the inheritance. After three years of fighting that included the bloody Battle of Fontenoy, they agreed to split the empire at Verdun in 843. Lothair got the middle strip — Italy, Burgundy, and a corridor running up to the North Sea. Charles the Bald got the western portion, which became France. Louis the German got the east, which became Germany. The middle kingdom, Lotharingia, was the weak link. It had no natural borders, no linguistic unity, and no political coherence. Over the following centuries it was carved up by its neighbors, and the territory it once covered — Alsace, Lorraine, the Low Countries, parts of Switzerland and northern Italy — became the most fought-over ground in European history. For the Church, the treaty meant the end of a unified political partner. Instead of one emperor to deal with, popes now had to navigate between rival kings, each claiming Charlemagne's legacy. This fragmentation would eventually contribute to the Investiture Controversy, the rise of national churches, and the political complexity that defined medieval Catholicism. The dream of Christendom as a single political entity died at Verdun, even if it took centuries to fully bury it.
Why it matters
Ended the unified Carolingian Empire and created the political map that would shape Church-state relations in Europe for the rest of the Middle Ages.
What Happened
After three years of civil war following the death of Emperor Louis the Pious, his three sons — Lothair, Charles the Bald, and Louis the German — divided the Carolingian Empire into three kingdoms at Verdun in 843. The western portion became the nucleus of France, the eastern portion became the nucleus of Germany, and the middle strip became the contested territory of Lotharingia. Charlemagne's unified Christian empire was finished.
Why It Still Matters
The Treaty of Verdun created the basic political geography of Western Europe that persisted, with modifications, into the modern era. For the Church, it meant dealing with multiple competing rulers instead of one emperor. The resulting complexity shaped everything from papal elections to crusade politics to the Protestant Reformation. The idea that Western Christendom could ever function as a single political unit was always more aspiration than reality, and Verdun is where that became obvious.