The whole time Omar the conqueror was directing the territorial expansion oflslam, Omar the spiritual leader was directing the consolidation of Muslim doctrine and defining the Islamic way of life. Abu Bakr had established that Islam was not just an abstract ideal of community, but one particular community with a world-changing destiny. Omar formalized this by declaring a new calendar that began, not with the birth of Mohammed, nor with the first revelations, but with the Hijra, the migration of Muslims to Medina. Omar's calendar enshrined the conviction that Islam was not just a plan for individual salvation, but a plan for how the world should run. Many religions say to their followers, "The world is corrupt, but you can escape it." Islam said to its followers, "The world is corrupt, but you can change it." Perhaps this was inherent from the earliest days of Mohammed's preaching, but Omar confirmed this course for Islam and set it on tracks of iron.