It was spread through business and trading.
First through conquest in the Persian Empire. But after that through individual Arab Muslim traders whom honesty and piety opened the doors to the heart of Asia.
When the Ottoman Turks conquered much of eastern Europe, they imposed heavy taxes on the Christians living under their control. Many of the wealthy converted to Islam to avoid the taxes.
how did islam spread in africa
If we take time as a measure of the spread of religion,then since its establishment ,Islam is the religion which spread or still spreading rapidly in Asia followed by Christianity.
To be entirely fair, it was Türkic Tribes of Central Asia who spread Islam to China, but the reason that Arabs spread Islam to Spain, Sicily, and India was that they genuinely believed it to be the correct religion.
The Middle Ages were already under way when Islam began to spread in Arabia. It spread to Persia and Palestine. Then it spread into India, across North Africa, into other parts of Africa, to Asia Minor, to Central Asia, Southeast Asia, to Spain, Sicily, Southern Italy, the Balkans, the Philippines, and Indonesia. There is a link below.
India, Africa and Southeast asia
Some of the regions where Islam spread include the Arabian Peninsula, North Africa, the Middle East, Persia (modern-day Iran), Central Asia, the Indian Subcontinent, and parts of Southeast Asia.
Islam religion is spread all over the world. However, Islam religion is major religion in the Middle East, North Africa, and Asia.
Judaism, Christianity, and Islam were all founded in southwest Asia, more specifically the Middle East.
Islam spread to the island of southeast Asia through traders and merchants. Many of the city states in Malaysia and west Indonesia had a strong maritime trading orientation and as a result, accommodated many Muslim merchants from Arabia, India, and the East African coast. As a result, the ideas of Islam became incorporated in those areas, supplanting the previous Buddhism. In the rest of Southeast Asia, such as Thailand, Cambodia, Laos, Burma, and Vietnam, the orientation was much more inland and river-based trade, meaning that Islam did not have the same inroads and access.
Sufi mystics
Christianity and Islam spread far from where they were founded
Asia - primarily in the south. North Africa A bit into Europe in Spain with the Moors.
Muslim merchants set up trading posts throughout southeast Asia and taught Islam to people there.