Islam spread more rapidly than any other major world religion. why do you think this was? what aspects of the religion made it appealing? how was the cultural climate conducive to the rapid expansion of islam?

It wasn't really Islam that was spreading. It was the Muslims and in their wake Islam. It was a simple enrichment of their own people. 
 
The Byzantine and Sassanid empires fell because they were exhausted of centuries of battles. 
The Jews and Christians of Syria and Persia nearly invited the Muslim conquerers inside because they were tired of religious battles locally.

It wasn't really Islam that was spreading. It was the Muslims and in their wake Islam. It was a simple enrichment of their own people.