Islam was founded on the dozens “Christian-Jewish” “Heretic sects” in the Near East
When the Byzantine Empire was established in Constantinople and adopted Christianity as an official religion, and later founded the “Orthodox Christian” sect as the religion of the empire in the mid of the 5th century, the hundreds of local based “christian sects” in Syria, Palestine and Lebanon were persecuted and had to transfer east of the Euphrates River (Persian Empire), the Arabian Peninsula, and further toward China.
The Prophet Muhammad was a member of one of those “Jewish-Christian” sect in Mecca and Islam was almost a copy/paste of the local Bible they used in Mecca, mainly most of the Jewish mythical stories, their prophets, and their customs.