What was the effect of Muhammad's death? 

After Muhammad’s death in 632, no one could legitimately claim to be the next prophet of Islam. As a result, his political authority was transferred to the umma with no established principle of succession.

This created opportunities for innovations but also caused deep divisions among the Muslims. The biggest innovation was the creation of the institution of caliphate, in which the leader of the community (amir almuminin) became the deputy (khalifa) of the Prophet. The first four caliphs (632-61) justified their powers on the basis of their close association with the Prophet and continued his work under the general guidelines he had provided.

The twin objectives of the caliphate were to retain control over the tribes constituting the umma and to raise resources for the state.