Very true, as described in "The Spread of Islam" by James Levi Barton.
An exerpt .....
"Until after the flight to Mecca [sic; the author certainly meant to write "Medina" (web editor)], Mohammed endeavored to propagate his new religion by persuasion rather than by force. His was a quiet, persistent search for favorable soil in which to sow the seed. After only eight years at Medina, when success had crowned his armed campaigns, the prophet is reported to have addressed a manifesto to the world inviting all mankind to submit to Islam. Ambassadors were sent to present these messages in person. Tradition declares that this message was as follows, quoting from the one said to have been sent to Emperor Heraclius:
In the name of God, the Merciful, the Compassionate, Mohammed, who is the servant of God and his apostle to Herclius the Emperor of Rome. Peace be on whoever has gone on the straight road. After this I say, verily I call you to Islam. Embrace Islam and God will reward you two-fold. If you turn away from the offer of Islam, then on you be the sins of your people. O people of the Book, come towards a creed that is fit both for us and for you. It is this - worship none but God and not to associate anything with God, and not to call others God. Therefore, O ye people of the Book, if ye refuse, beware. We are Muslims and our religion is Islam."
This would indicate that Mohammed saw a vision of world conquest for his new religion, and so began by asking certain sovereigns to accept him as a prophet Of God, and inviting all the world to the same privilege. From this time onward, the sword played a large part in the dissemination of Islam.
While Mohammed set out to found a new religion, he also established a new political order, different from anything that then was or that had previously existed. Starting with the idea that he wished only to convert his brethren to belief in one God, he overthrew the government of both Medina and Mecca, and, for the tribal rule by which the leading families shared in the conduct of public affairs, he substituted a theocratic monarchy centering in himself - the representative of God on earth.
Missionaries with the sword multiplied their activities, as success crowned their endeavors, to win neighboring tribes. Biographers of saints report that vast numbers were converted by the power of preaching the Gospel of Mohammed, although it is difficult not to believe that, in many instances at least, if reports are true, an army was waiting to strike in case the preacher's eloquence and persuasiveness failed to bring about the desired results. It is impossible to distinguish, in the narrative of the many conquests of Islam during the first century after the death of Mohammed, how much was due to religious zeal and how much to greed and political ambition.
Other methods have been employed by Mohammedans for propagating their faith, such as the purchase or forcible seizure of non-Moslem children in times of plague, famine, war and massacre, or even in times of no special disturbance, and rearing them in the Mohammedan faith. The Janissaries at Constantinople are a case in point. The children of Christians were taken regularly to replenish the ranks of this special body-guard of successive Sultans of Turkey. Another method employed to increase the number of ******* was the plurality of wives and the use of captive women of non-Moslem races as concubines. These two methods of propagation were conspicuously employed, and even to the present time are in use by the Turks."