Answer:
caliph
Step-by-step explanation:
After the death of Muhammad, the Muslim Empire was inherited by caliphs. They divided the empire into several parts, but they still collaborated most of the time, and usually acted together when it came to military conflicts. The caliphs created caliphates, some of which grew very strong and contributed a lot to the spread of Islam, while some where less successful. The caliphates existed up until the Mongol invasion when they were totally destroyed and never managed to recuperate from that blow.