Why did an Islamic empire develop and expand so quickly?

It expanded, due to military conquest, trade, and more territories. Have a nice day! :)

Explanation:

The success of the Muslim's was because they had weakened the Byzantine and Persian empires. Belief in Islam and also the desire to glorify the new religion encouraged the Muslim armies to win their fights, and when the empire began to expand so did the religion of Islam. Many of the people in the newly conquered areas were treated fairly by the Muslim leaders. But some of the people that believed in other regions were given extra taxes. That is when people began to covert to Islam, so they could gain political or economic advantages. Other citizens were intrigued to Islams simple and direct message. Other people were intrigued by the religion not having a hierarchy or class of priests, and the religion accepts all believers, regardless of race, gender, class, or wealth.

Explanation:

the answer is a new goverment.