How did internal conflict and outside threats shape European political and economic development in this period?

The large-scale division of Charlemagne’s empire into three parts in the ninth century led to a decentralization of power at the local level. Civil wars weakened the power and prestige of kings, who could do little about domestic violence. Likewise, the great invasions, especially those of the Vikings, weakened royal authority. The western Frankish kings were unable to halt the invaders, and the local aristocracy had to assume responsibility for defense. Thus, in the ninth and tenth centuries great aristocratic families increased their authority in the regions of their vested interests. They built private castles for defense and to live in, and they governed virtually independent territories in which distant and weak kings could not interfere. Common people turned for protection to the strongest power, the local counts, whom they considered their rightful rulers, and free peasants sank to the level of serfs.