At first, Mohmad tried to pass himself off as the last prophet making way for the return of Christ.
That didn’t wash. He never managed to get more than his own household into the “religion” he was making up as he went along.
Then, he approached the bandit tribes that lived in the desert around Mecca and Medina. He offered them a religion that gave full permission of “god” for theft, rape, murder and all the usual bandit practices.
That’s when Islam took off and started getting converts.
When did first become bandits?