The Jihad
Islamic attempts to spread the religion of Islam to other lands and peoples is known as Jihad. Those caliphs who follow the word of Mohammed, kept in touch with the believers of Islam, and asked the advice of other leaders known as The the Rightly Guided Caliphs. Historically, these caliphs sought to defend, protect, and spread Islam beyond the realms of the Arabian peninsula.
Arab militia spread outward and gained land in Iraq, Egypt, Persia, Palestine, and Syria. They were successful for many reasons. They were united by their faith and determined by the goal, which to them, was what the Quran dicated. The economic standing of the nations defeated by the Muslims was weak, as well as their social status and military power. Forcing them into conversion to Islam was not a difficult task once they had invaded and already the fallen empires were unstable and vulnerable.
According the the Qu'ran, Muslims had a religious duty to adhere to the rules of the faith by struggling for the propagation of their religion. The Quran actually prohibited the introduction of Islam to others by force. Islamic teachings, however, contradictorily said that warriors who died in the Jihad would immediately enter paradise, because they were fighting for the selfless cause of expanding the religion.