The capture of Iraq’s second largest city by a multinational Islamist militant group last week sent shockwaves through the region as the crisis in Syria escalates into religious warfare across the Iraqi border. Once known as “The City of Two Springs” for its temperate climate and high livability, Mosul now finds itself at the center of a polarizing religious conflict that threatens to tear the fragile war-torn state apart.

The Islamic State in Iraq and Syria (ISIS) is a Sunni militant group active in Syria and northern Iraq that originated as a subgroup under Al-Qaeda. Though nearly 97% of the population identifies as Muslim, Iraq is far from a religiously homogeneous state. Its Muslim population is bitterly divided between a Shiite Arab majority concentrated in the south, and a Sunni Arab minority located primarily in the north. As the world’s largest Shiite country, Iran has a strong interest in halting the advance of ISIS, which aims to overthrow Iraq’s Shiite-dominated regime led by Prime Minister Nouri al-Maliki. For the better part of a decade, Iran has taken an active interest in improving ties with al-Maliki’s government. These policies of rapprochement have been largely successful in transforming Iran from Iraq’s bitter enemy into its leading trade partner. Yet the relationship Iran has painstakingly developed with the incumbent regime in Iraq is now gravely threatened by ISIS, which seeks to revise the religious balance of power in the region. In a move that signaled the growing resolve among Iran’s leadership to protect its interests in Iraq, Iranian President Hassan Rouhani condemned the group as “acting savagely” and asserted Iran’s readiness to “combat” the rising militant threat.

For very different reasons, the United States now finds itself arriving at the same conclusions as its longtime foe, Iran. Just three years ago, President Barack Obama withdrew the last American troops from Iraqi soil. But to the great distress of the administration, which worked diligently to transition the responsibility for security in Iraq to the Iraqi Armed Forces, the democratic institutions established at heavy cost to the American people are already in danger of being overthrown. The possible deterioration of the situation into civil war would damage both the reputation of the United States abroad and have serious electoral consequences domestically. Yet it is difficult to imagine a scenario in which an administration whose electoral mandate was ending American military involvement in Iraq would betray its commitment to exercising restraint in foreign affairs.

Though the United States and Iran share an interest in ensuring the survival of the Iraqi government, they diverge in the methods they are capable of using to achieve their common goal. While the United States is unenthusiastic about the prospect of dragging a war-weary American public back into a serious conflict, Iran has already shown a willingness to deploy its forces on the ground, sending several battalions of its Revolutionary Guard to reinforce Baghdad. Likewise, the United States has technological advantages at its disposal that Iran cannot offer, and has the diplomatic clout necessary to work with other strong states in the region such as Turkey, Israel, and Saudi Arabia. It is for these reasons that cooperation between the two countries could offer the greatest chance for preserving the stability of Iraq. A combination of Iranian military forces and American soft power could give the government of Nouri al-Maliki the support it needs to overcome the difficult challenges faced by the young democracy. Moreover, an exercise in coordination between two historic enemies with very little common ground could provide a foundation for future dialogue by establishing a level of trust. In the context of the ongoing nuclear talks between Washington and Tehran, such a solution could prove invaluable to the successful negotiation of future agreements.

In the meantime, as the American, Iranian, and Iraqi governments struggle to formulate their responses to the gravest threat Iraq has faced since the U.S. occupation, the forces of ISIS, bolstered by their unprecedented victory in Mosul, are on the march. With large swaths of Syria and Iraq now under their control, the road to Baghdad is clear.

Lefteri Christodulelis is a recent graduate of The University of Texas at Austin. His background is in politics, history, and international relations. He is also quadrilingual, speaking Chinese, Greek, and Spanish.