The Crusades are at the center of Medieval History, whether we consider them the most thrilling and inherently romantic Christian adventure or the final of the barbarian invasions. Before the Crusades began, the center of our civilization was in Byzantium and the countries of the Arab Caliphate. Before they faded away, the hegemony of civilization had passed to Western Europe. From this transfer, modern History was born. However, in order to clearly understand this issue, we must comprehend not only the specific conditions in Western Europe that led to the Crusader impulse, but - perhaps even more so - the circumstances in the East that paved the way for the Crusaders and facilitated their advance and retreat. We must also take into account what was happening from the Atlantic to Mongolia. If we view history only from the perspective of the Franks or only from the perspective of the Arabs or even only from the perspective of their main victims, the Christians of the East, their significance will elude us. Because, as Gibbon concludes, the History of the Crusades was the History of a Global Conflict.