At the close of the 11th century, war consumed Europe and the Middle East in equal measure. In 1095, Byzantine Emperor Alexios I Komnenos appealed to Pope Urban II for military assistance against the advancing Seljuk Turks, whose empire had been consolidating control across Asia Minor and the Middle East for four centuries and now threatened to push into Europe. The Pope's response — a call to arms directed at all of Western Christendom — united kingdoms that rarely agreed on anything against a common enemy. Crusades: Book I covers 1096 to 1148, encompassing the First and Second Crusades and the volatile period between them. Command the allied forces of the Crusader cause — Byzantine armies and the Kingdom of Jerusalem — or take command of the Seljuk Turks and their allied Muslim forces as they work to repel the invasion. The fate of Christendom, or the integrity of the lands defending against it, rests on the orders you give.