France and Germany were "united" in the Carolingian Empire, which broke up after the Treaty of Verdun in 843. The eastern part, aka Germany, went to become the Holy Roman Empire, a somewhat confederal empire stretching from Germany to northern Italy. The western part, aka France, became in the following centuries a solid nation state, which identity became solidified after multiple wars with England. France was more influenced by Roman culture and language, while Germany had a much smaller Roman influence.