How did Islam expand rapidly after the fall of the Roman empire?

The correct answer is **C. Islamic empires joined together nomadic groups and small, local kingdoms that were left in a vacuum of power caused by the fall of the Roman empire**.

After the fall of the Western Roman Empire, there were significant power vacuums across the regions that were once under Roman control. The rise of Islamic empires capitalized on this disarray, facilitating rapid expansion through military conquests, trade, and the appeal of the new Islamic faith, which attracted various local populations and often integrated existing social structures.