Will mark brainliest -how did islamic culture and religion spread so quickly? (two ways)

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.

hope this helps you(:
  

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