The two parties have actually come a long way since the worst days of their internecine conflict. After 2003, they completed a reconciliation that had begun earlier with American support, and both secured their legitimacy by participating in elections that were seen as largely free and fair. The two parties, along with an opposition group named Gorran (itself a splinter of the P.U.K.), belong to a coalition government in the Kurdistan region.

As the advance of the Islamic State has shown, this accord no longer goes far enough. The Kurds must unify militarily if they are to contain the jihadist threat and secure their region from the kind of terrorist atrocity that Erbil witnessed just over three weeks ago, when suicide bombers struck the governor’s office and killed at least six people. A unified security force would be far more effective in fighting the Islamic State’s battle-hardened units. If pesh merga forces in Sinjar had been operating under central authority, they might in fact have held the town.

The Islamic State also proved that the Kurds remain heavily dependent on international support. This reliance is not sustainable. Once the immediate threat from the Islamic State has passed, long-term support from the international community is not realistic. The recent rush of aid does not signal a major shift in Western foreign policy toward Kurdistan.

The political reconciliation that has taken place is just one element of unification, and a relatively fragile and reversible one. To ensure that the Kurds never again fall into civil strife, the two main parties must reform the structure of the military command.

The pesh merga can no longer be a security force with divided loyalties. Both on the battlefield and behind the lines, the pesh merga must evolve into a professional army that is answerable to the regional government and its Parliament, rather than partisan elites.

The United States and the international community need to support the Kurds in this process. Erbil is already a regional center for diplomacy and business, but there must be a more engaged, less laissez-faire approach on the ground from the Kurdistan region’s international allies. It is in their interests, too, to see a transformation of Kurdistan’s armed forces into a more effective partner in the fight against the Islamic State. A centralized, professionalized pesh merga would also be a model for the region’s other Kurds who are fighting the jihadists, like the Syrian Kurdish forces around Kobani.

A unified military would help prevent the two parties from entrenching themselves in unyielding positions, and so reduce the risk of renewed hostilities. The lack of military unity has also undermined the judiciary, the independence of the media and the political process. Reforming the pesh merga command will strengthen the rule of law in the region more generally.

In the end, unity alone can truly insulate the region from the threat from the Islamic State. Without it, it is much harder to imagine the Kurds’ achieving the statehood that most, if not all, want.