There are about 250,000 of this Shia Muslim group, also called Madan, living in Iraq.
They originally lived in the marshes around the southern end of the Tigris and Euphrates rivers.
After the first Gulf War, they tried to overthrow Saddam. The Iraqi government stopped them.
Saddam's government decided to drain the marshes, which split up all the Madan. This removed their ability to threaten the old regime.