What was the most important factor in the division of Muslim society into four parts?

The most important factor in the division of Muslim society into four parts—Sunni, Shia, Khawarij, and Sufi—was the dispute over leadership and authority following the death of the Prophet Muhammad. This disagreement primarily stemmed from differing opinions on who should succeed him as the rightful leader of the Muslim community. Political, theological, and cultural differences further solidified these divisions over time, leading to distinct practices and beliefs within each group.