one reason is that Arab armies were united by their beliefs.Islam taught that Muslim warriors who died in the service of Islam would win a place in paradise.the idea of jihad also motivated many Muslim soldiers.the lure of riches to be won in the conquered lands was another powerful incentive. and answer 2 Islam was both a religion and a political entity. While the religion was not
often spread by "Convert or Die" pronouncements (such as was the case in Christendom), Islam as a political entity was spread by armies and warfare. In general, the following reasons account for the spread of Islam both politically.and religiously hope this helps:)
