Soldiers with the Kurdish Peshmerga wait at an outpost on the edges of the contested city of Kirkuk, Iraq. Photographer: Spencer Platt/Getty Images
Soldiers with the Kurdish Peshmerga wait at an outpost on the edges of the contested city of Kirkuk, Iraq. Photographer: Spencer Platt/Getty Images

Thanks to the Iraqi military's chaotic flight from Mosul in June, jihadists from the Islamic State are now armed with abandoned U.S. weapons and armored vehicles. Iraq's Kurds -- arguably the most reliable U.S. allies in the Middle East after Israel and Turkey -- are not.

The implications of this bizarre mismatch between U.S. arms and interests has become clear in recent days as Islamic State militants have driven Kurdish Peshmerga fighters from several towns near Mosul in northern Iraq. The Sunni extremists acquired two oil fields, and they are fighting to seize a dam that supplies water and electricity to much of Iraq. Tens of thousands of residents of the Yazidi religious minority have fled for their lives.

Of course, President Barack Obama's administration does not bear primary responsibility for the mess in Iraq, whatever partisan critics may say. Yet its response to the rise of the Islamic State, now the most urgent threat to stability in the Middle East, has not been up to the challenge. The U.S. remains focused on preserving a unified Iraqi state, even as events on the ground have obliterated cooperation among Iraqi Shiites, Sunnis and Kurds.

The priority is to crush the Islamic State. That requires some difficult decisions -- for example, arming the hard-to-control rebels across the border in Syria who are also fighting the Islamic State, and intervening on behalf of an ineffective Iraqi government in Baghdad that bears much of the blame for the country's sectarian disintegration. In this context, selling weapons to the Kurds is a relatively easy call. There is no chance the Kurds would pass the weapons on to jihadists. Nor would they use their firepower to slaughter innocent civilians from other faiths or ethnic groups. The Peshmerga are easily the most disciplined fighting force in the region.

When asked about arming the Kurds, U.S. officials talk instead of their efforts to "coordinate" between Kurdish leaders and the government in Baghdad. They rely on legalisms to explain why they still prevent the Kurds from financing the war effort by selling oil on the world market. But Iraqi Prime Minister Nouri al-Maliki refuses to share weapons with the Kurds. And tankers carrying Kurdish oil are stranded from the Gulf of Mexico to Singapore because the government in Baghdad insists on its right to sell all of Iraq's oil.

Maliki fears that if the Kurds are given money, tanks, body armor and other weapons, they would later use them to make a bid for independence. His fear is not unfounded; the Kurds certainly want independence. But this line of argument puts the cart before the horse. Unless the forces of the Islamic State can be rolled back, Iraq is finished as a unitary state in any case.

And while keeping Iraq intact remains a worthy goal, the prospect of a Kurdish state is no longer the threat to stability it was a decade ago, when Turkey would have invaded to prevent it.

The ideal way to defeat the jihadists of the Islamic State would be for the Iraqi armed forces, the Kurdish Peshmerga and, eventually, Sunni tribal leaders to fight together. Unfortunately, however, Maliki has demonstrated he would rather rely on support from Iran and sectarian Shiite militias than cooperate with potential rivals.

The U.S. need not make the same mistake. It should help the Kurds to secure the funding, weapons and ammunition they need to defend themselves and hold the line against the Islamic State in the north. If not, U.S. weapons will be used to defeat U.S. interests as well as the Kurds.

To contact the senior editor responsible for Bloomberg View's editorials: David Shipley at davidshipley@bloomberg.net.