Complex sentence: From the 420s onwards, headed by a certain Chlodio that expanded their territory to the Somme into northern France, they formed a kingdom in that area, with the Belgian city of Tournai becoming the center of their domain.
Split into simpler sentences: From the 420s onwards, headed by a certain Chlodio, they expanded their territory to the Somme into northern France. They formed a kingdom in that area with the Belgian city of Tournai becoming the center of their domain.