Final answer:
The second caliph, Umar, introduced a bureaucracy to unify and administer the vast Islamic empire. This included the diwan, which managed taxes, public safety, and the application of sharia law, among other functions.
Step-by-step explanation:
The caliph introduced a bureaucracy to help unify the empire. During the reign of the second caliph, Umar, who succeeded Abu Bakr in 634, he gave the Islamic state an administrative structure to handle its vast territorial expanse. Umar created the diwan, a state bureaucracy with different departments for tax collection, public safety, and the exercise of sharia law. This system was crucial for the management of the diverse and rapidly expanding empire, which included areas formerly part of the Byzantine and Persian empires. As the empire grew, the Umayyads and later the Abbasids continued to develop and expand these bureaucratic institutions.