Strictly speaking, every event, if old enough, has affected world history. Even the smallest occurrence has an impact which propagates itself such that eventually every person is in some was impacted by it. However, certain events have had affects on world history far greater than would be suggested by the extent to which they are remembered today. One such event is the Battle of Fontenoy, which was fought on June 25th, 841.
The Battle of Fontenoy was the culmination of the Carolingian Civil War, a three-year-long conflict fought between the three sons of Louis the Pious, the son of Charlemagne and King of the Franks. Before his death, Louis had divided his kingdom into three parts in accordance with Frankish inheritance laws. Lothar I, king of the middle third of Louis’s realm and the son who had been given the imperial title, wanted to unify his father’s lands under his rule. Charles the Bald and Louis the German, kings of the Western and eastern portions of the realm respectively, opposed his efforts and so raised armies to meet him in battle. The battle initially went in Lothar’s favor. However, the arrival of reinforcements on his brothers’ side allowed Louis the German to push him back and when force s under Bernard of Septimania arrived Lothar’s army was routed. he survived and was able to return to his territory, but would be forced to abandon his capital and sue for peace in the next few years.
The Battle of Fontenoy led to the creation of the modern nation-states of Europe. The survival of west and East Francia as independent kingdoms led to the formation of modern-day France and Germany. While middle Francia would not survive, constituent territories like Northern Italy and Bavaria would develop into modern states and regions. The battle ended any real chance of a unified Europe during the Middle Ages, and led to a Europe made up of disparate and opposed nations whose interactions and conflicts drove history for a millennia.