According to the belief of Shiite school of thought, Imam Mahdi (Imam Zaman or factually 12th Imam of Shia)) will reappear as the last Imam of Shiite. They believe that he will come to save the world from oppression. According to the hadiths, many people will join his as his soldiers.
My question is that who will be his soldiers to help him to fight against oppressors? In fact, will all of his soldiers be Shiite or is it feasible that many other people join him from other sects or even from other religions?
Note: I'm looking for the answer from Shia's perspective.