Final answer:
Muhammad, after facing rejection in Mecca, migrated to Medina in 622 CE in the event known as the Hejira. In Medina, he established a community and became its leader, which led to the growth of his support and army. Eventually, he successfully returned to Mecca, converting it into the center of Islam.
Step-by-step explanation:
Upon facing opposition from the city leaders of Mecca, Muhammad was compelled to leave the city in 622 CE, an event known as the Hejira. This marked the beginning of the Islamic calendar. Muhammad and his followers fled to Medina, where they found refuge and a receptive audience. As their numbers grew, Muhammad established himself as both a religious and political leader in the city.
In Medina, Muhammad formulated the Constitution of Medina, creating an alliance with the local Arabs and Jewish tribes, ensuring mutual protection and the establishment of a community under his guidance. This new ummah did not distinguish between religious and political authority, which was critical to its success. Muhammad's teachings continued to attract more supporters, eventually allowing him to form an army and engage in battles with the Meccan forces.
Between 625-630 CE, multiple battles ensued between the Muslims and the Meccans. Ultimately, Muhammad was victorious, and he returned to Mecca in 630 CE. Upon returning, he entered the Kaaba and destroyed the idols within, reestablishing the worship of the one God - Allah - and making Mecca the center of Islam. Muhammad's victory was significant, as he converted his former opponents and unified the Arab tribes under the banner of Islam.