The correct answer is: Islam spread through religion, trade, and military effort that expanded across multiple continents.
This response accurately summarizes the development of Islam into Islamdom by highlighting the various means through which Islam expanded. It acknowledges the roles of religious conversion, economic interactions through trade, and military conquests that contributed to the establishment and spread of the Islamic Empire across Asia, Africa, and parts of Europe. The multifaceted approach reflects the complex historical factors that facilitated the growth of Islam as a dominant political and cultural force.