What were the three major cities in the Islamic world?how did each develop and grow to become important?

Answer 1

http://www.threes.com/index.php?option=com_content&view=article&id=2077:three-holy-sites-of-islam&catid=81:religion&Itemid=61

Read carefully and take good notes.

Then look up each one separately if you need more information.

Answer 2

What were the three major cities in the Islamic World