Estimates put the fighting strength of Isis in Syria and Iraq at around 7,000 but its numbers in Iraq appear to have been bolstered by other groups, including local Sunni militants and Ba’ath nationalists particularly in Tikrit. Despite claims that they have captured helicopters in Mosul, it seems unlikely they would be able to deploy them. Lightly armed with Toyota pickup technicals, RPGs and small arms, Isis has captured some armoured Humvees, although there are suggestions that some equipment has been sent back to Syria. While they have been able to operate easily in largely Sunni areas where they have some support from a population angry and alienated from the Shia-led government in Baghdad, the capital is a different proposition. One district alone, Sadr City, has a Shia population of some 1 million and since the sectarian war that ended in 2008, the sprawling suburbs have been divided along sectarian lines with checkpoints and barriers.