Here is an illuminating story from The Telegraph:
…there is no disguising the fact that hundreds of angry young Shias – some poor and ill-educated, others from relatively well-off families – are flocking to the Mahdi army.
The article concludes:
“I am no fan of Moqtada al-Sadr but it is the Americans who are causing our suffering. Every day they kill innocent people. They should just leave our country. They promised democracy and freedom but all they have delivered is torture and abuse.”