Iraq is rapidly sliding into an all-out civil war that is likely to spill over into neighbouring countries, resulting in mass deaths and refugee flows, serious disruption of Gulf oil supplies and a drastic decline in US influence in the region.

This grim forecast is set out in Things Fall Apart, a 130-page report released on Monday by the Brookings Institution’s Saban Center for Middle East Policy that also recommends how the US might contain the disastrous consequences of “spillover”.