period of 750 years in which Islam was spread to nations by trade. Unlike conquest, when Islam was spread by trade, there was a smaller chance of the people reverting to their original beliefs. Thus, this mode of conversion was more effective than spreading Islam by the sword and the Islamic rulers understood this. That is why they gave a lot of encouragement to trade activities.
Even in the early period of Islam, most of the conversions to Islam, that did not happen by conquest, were because of contact with Muslims in cities that fell on the trade routes.