His judgment is that it won't for the following reasons:
1) Iraq has experienced a quarter century of warfare. This means that
a) The country and in particular the political elite are tired of fighting -- they will be reluctant to escalate the conflict.
b) Most Iraqi men have some degree of military experience and are armed. This means that there are no vulnerable prey populations. Neighborhoods and religious communities have the means and will to defend themselves.
c) The existence of numerous armed militias jostling for power, has prevented the majority Shia from organizing on a scale necessary to wage an all-out religious war against the Sunnis.
2) The presence of U.S. forces in Iraq. This means:
a) No other outside sponsor can intervene in Iraq with sufficient force to disturb the prevailing balance of power there. Iran and Syria can provide low-level support to specific groups, but cannot escalate that support without risking direct and major confrontatation with the United States.
b) The U. S. has become generally recognized within Iraq as the guarantor of the peace -- ensuring that no group becomes dominant and that outside forces are kept at bay.
In other words the situation is static, so long as the US maintains sufficient forces in Iraq.
He suggests that sufficient US presence would entail a force large enough to continue training the ISF and to constitute a "tripwire" in case of foreign interference.
[T]o gauge the likelihood of a genuine civil war occurring in Iraq one must look as much to Teheran, Riyadh, and Washington as well as Baghdad. Sectarian hatred may be necessary to fuel a civil war; but militarily speaking, it is not sufficient. And at least for the moment in Iraq, without the deliberate and massive connivance of outsiders, a genuine civil war is not in the offing.Read the whole thing here.
The key point to make here is that the continuing presence of US forces in Iraq is the best guarantee of stability there and throughout the region.