The strange defeat of the Iraqi army by the Islamic State of Iraq and Syria’s (ISIS) has caught American policymakers flatfooted. Aside from hand-wringing and outrage, they have had little to offer beyond recycled policy prescriptions for ethnic conflicts from the last two decades: partition, power sharing, or another “surge.” Each is unable to address Iraq’s coming anarchy. The only viable solution is a decisive military victory for one side over the other. Despite our historical animosity with Iran, it is in our national interest that Tehran prevails over ISIS.

The oppressive tendencies of the Maliki government have contributed to Iraq’s internal security dilemma. When ethnic groups that are weakly or corruptly governed compete for safety, they may feel compelled to fight. This is because they might be uncertain about each others’ motives or military capabilities, or they do not believe that the other side can keep its promises to abide by a peace agreement.

Partition has been proposed as a solution to ethnic conflict. In an editorial in The New York Times in 2006, then-Sen. Joe Biden and President of the Council on Foreign Relations Leslie Gelb proposed a federal solution for Iraq. This would have devolved powers broadly to each of the regions, amounting to a “soft partition” of the state. International relations theorists have found partition to be an attractive solution to sectarian conflict in situations where the state has collapsed and ethnic groups are operating in a self-help world.

However, partition does not guarantee conflict will not recur among the states created out of the rump of Iraq. Take India and Pakistan. After the initial war that led to their separation in 1947, they fought again in 1965, 1971, and 1999. This is not to mention the additional skirmishes and Militarized Interstate Disputes (MIDs) that have occurred along the way.   Furthermore, Iraq does not exist in a vacuum; like it or not, it is part of the same battlefield as Syria and Lebanon. Any partitioning of Iraq will have repercussions for those states as well as minorities residing in Turkey and Iran.

A popular idea that seldom works is power sharing. It’s popular because it is synonymous with mature, liberal democracy. It’s ineffective because neither side trusts the other once it disarms. The majority of these arrangements fail without a third-party guarantor to keep the peace, vigorously monitor the terms of the agreement, and allow each side to keep some of its weapons. There is no neutral third-party monitor with the authority or resolve to fulfill to such a role when it comes to Iraq.

Sen. John McCain has suggested President Obama sack his entire national security team and bring back former Gen. and CIA Director David Petraeus. This implies that America should give the troop “surge” another try. There are two problems with this prescription. First, the “surge” was successful because of the interaction between the increased level of American troops in Iraq AND the Anbar Awakening. The two were individually necessary, but jointly sufficient for the temporary decrease in violence. Maliki and Co. have alienated the Sunni community by dismembering the Awakening Councils and forcing the country’s Sunni Vice President into exile on trumped-up criminal charges. Second, while Americans are outraged at ISIS’ unexpected victory, it is doubtful that the takeover of Mosul and Tikrit has shocked them into supporting the sending of troops back to Iraq.

According to James Fearon of Stanford, since 1955, 75% of the civil wars that have been fought for control of a central government were concluded with one side obtaining a decisive, lop-sided victory. Such outcomes eliminate any uncertainty as to the distribution of resolve or military capabilities between two (or more) groups as well as the commitment problem that is responsible for conflict in the first place. Iranian President Hassan Rouhani has signaled that he is ready to cooperate with the U.S. against ISIS. The Obama Administration should help tip the military scale in his favor.