“United by Islam, Arabs preached their religion and expanded their rule across Southwest Asia and to many othe parts of the world.” p.453 My World history (Early Ages)

Islam did not unite Muslems, as noted by the early split (7th century ) between Sunni Muslims and Shia Muslims. What united Muslims then and now is the most common denominater among Muslims -war against the non-believer. War, the booty of war, slavery, pillage, and conquored lands increased the first followers of Muhammad by a thousnad times. Religious practice is only twenty percent of Islamic teachings. Eighty percent of Islamic practice is Jihad (war) When Muslims have total control of a country and have no non-believers to war against, they war against themselves -fundmentalists against moderates. And then, Men war against women.

Notice the textbook connection between the word preached and expanded. This is intentional, in order to plant that false association in the mind of a child. Islam never expanded in the world by preaching.