Izen, as I read somewhere, just after a year of Mohammed?s death, his successors securely held Arabia to invade Byzantine Empire and Persia. They defeated Byzantines in 635 AD in Damascus, which led to subsequent invasion of Mesopotamia, which had remained largely Arab ethnically. Persia was also defeated in the hands of the Muslims and the people were converted to Islam. Conversion was rapid in urban regions while slower in rural areas, where the peasantry did not converted completely until the ninth century. I have included the image of cuneiform, a wedge shaped form of writing developed by the Sumerians:- Image source:- http://www.historyguide.org/images/cuneiform.jpg