And Byzantium and Spanish Islam could deploy armies quite effectively. This lead to the crusades, a series of Western military expeditions against Islam. The idea was extended, and the longstanding war of Christians in Spain against Islam was included as a crusade. Eventually even wars against pagans in Eastern Europe were included. In 1204, the Fourth Crusade was diverted, Constantinople was conquered, and the Byzantine Empire destroyed as a major power.
Trade routes become more active.
Largely a result of Church preaching that the Jews were devilish and responsible for the death of Jesus. During each of the major 12th-century crusades, crusaders in the West attacked and killed Jews. Jews were expelled from France, England, and eventually Spain. In 1209, Pope Innocent III authorized a crusade against the Cathars in southern France. We cannot ignore the many wars between states, between noble elites, and within countries.