Don't underestimate the efforts of Muslim traders. This is how Islam spread to most places. If you look at a map of the Muslim world, it is far wider than any of the military conquests. In fact India, where Islam had it's most successful militarism, is not considered part of the Muslim world. Regardless, the most populous Muslim nation was converted through trade and culture. So was most of West Africa. The Muslim traders even worked on the nations that became the caliphate. Trade conquered the Turks as well.