Islam spread so much due to the expansion of trade and commerce.
Explanation:
Prophet Muhammad (PBUH), the founder of Islam had been a merchant himself thus the role of a merchant was accorded immense importance and respect in the Islamic society. The Quran, holy scripture of muslims also promoted the business of trade and commerce.
The spread and growth of Islam to various different places was conducted by expansion of trade. The muslim traders went to West Africa and also to Malaysia and Indonesia where Islam spread rapidly and people converted themselves to muslims.