Who are the insurgents in Iraq?

"Diverse groups have been drawn into the ranks of Iraq's insurgency, with little in common beyond a commitment to attack US forces or their perceived allies.

The insurgency has no single spokesman, nor any shared long-term aim. Where some groups, for instance, are fighting for a Sunni Muslim caliphate, others foresee a Shia theocracy for Iraq.

The incentives driving individual insurgents are equally disparate - from religious zeal to economic gain, nationalist fervour and anger at the loss of income or loved ones to the conflict.

There is little agreement on the numbers involved. Estimates vary from 30,000 to some 200,000 fighters - a figure cited by Iraqi intelligence in 2005.

Central Iraq's Sunni Muslim heartland is regarded as the crucible of the insurgency - scene of the bloodiest attacks and source of most of the fighters."
BBC