The period of 600CE to 1250CE was a period of religious spread and expansion. After centuries of being spread underground and evangelistically, Christianity finally reached a point of being the dominant religion from a Eurocentric point of view as the Catholic Church came into power. For a long time, Christianity had no association with a specific race or group, so it was spread peacefully through missionaries.
The best-known way was through monasticism, individuals who gave up their life for God and spread the Gospel throughout Europe, serving as a moral example. However, once the Catholic Church took control of Europe, Christianity began to be associated with the European Aryan race and the European kingdoms. As history progressed, Christianity took on an imperialistic view and spread Christianity by force.
Where Islam is similar to Christianity is that they also used missionaries. Sufi Muslims were effective missionaries as they stressed a personal relationship with Allah and a unique way to connect rather than a particular ritual. However, the spread of Islam is best known for its spread by force. The pillar of Islam, ‘jihad,’ which means the struggle to convert, was interpreted by many as a call to spread Islam by military conquest and expansion. Particularly after Muhammad’s death, the first four caliphs sought to expand the Arab empire and spread Islam. The conquered territories of Syria, Egypt, North Africa, and even Spain were not forced to convert, but those who did not were taxed significantly, leading to an increase in conversions alongside the belief that Islam was the answer to their problems.