Outlaw,

After the summer offensive started Ayatollah Sistani made a call for men to join the security forces. Supposedly tens of thousands signed up. The militias also mobilized and had been recruiting since around April of this year. I don't think the manpower is the issue, its the lack of training and competent officers to lead them. A recent U.S. military report said around half the army units were filled with militiamen showing their penetration into the ISF as well.