ERBIL, Iraq — Just a few dozen soldiers with automatic rifles and an old Humvee guard the Kurdish front line against ISIS.

This Kurdish outpost near the Mosul Dam is attacked several times a day, every day. So far, ISIS has sent twenty car bombs to try to destroy it. The Kurds are hanging on, barely, and are increasingly frustrated. They want to know why the U.S. — their ally — isn’t helping more or supplying the guns and ammunition they seek.

But Washington isn’t ignoring the Kurds out of spite. It’s dragging its feet out of concern that those weapons would not just be used against ISIS and would eventually, serve another cause: Kurdish independence.

Fight ISIS or fight to keep Iraq together?

To hear President Barack Obama and Secretary of State John Kerry describe it, the war on ISIS sounds straightforward. The vicious terrorist group has spread through Syria and Iraq and is slowly killing both nations.

ISIS has often been described as a cancer. The U.S. air campaign is designed to destroy the cancer and heal the nations it infected. But ISIS has insinuated itself along old, unresolved fault lines in Iraq. And nowhere is this plainer to see than in Kurdistan — or northern Iraq, as the government in Baghdad calls it.

The U.S. military has a special alliance with Iraq’s Kurds. Unlike the Arabs — both Sunni and Shiite — the Kurds have never raised arms against U.S. troops. In fact, even before the U.S. invasion in 2003, the Kurds have been unabashedly pro-American.

Erbil — the Kurdish capital — is unique in being an Iraqi city where you can see American flags hanging behind the cash registers at shops and restaurants. The Kurds believe that a strong relationship with the U.S. is key to achieving their ultimate goal of independence.

Kurds, who make up about 17 percent of Iraq’s population, are members of an ethnic group often referred to as “the largest stateless nation.” Their historical homeland is divided between Syria, Iran, Iraq and Turkey. Kurds spent the past century demanding, fighting and dying for the right to a free and independent homeland. Now, at last, that dream seems within reach.

During the U.S. war in Iraq, the Kurds were constructive partners in a fragile three-way government with their Sunni and Shiite neighbors. But the Americans have gone and ISIS has ended the illusion of Iraqi unity, leaving the Kurds free to declare their lands as their own.

As ISIS fighters marched through one Iraqi city after another last summer, Iraq’s army withdrew in advance of their arrival. While Iraqi forces ran away, the Kurdish forces — known as Peshmerga — grabbed the city of Kirkuk and its vast oil fields.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

It was a hugely important moment. Now that they have the city, they have no intention of giving it back to the central government in Baghdad, which they see as corrupt and sectarian.

The Kurds believe Kirkuk’s oil will make the autonomous Kurdish region in northern Iraq an economically viable, even wealthy, state. Control of Kirkuk is the key to nationhood that Kurds have always sought.

There is a formal referendum coming on the fate of Iraqi Kurdistan. Before ISIS came along, Kurds might have seen the benefit of keeping their uneasy alliance with the Iraqi state. They needed the money that the central government was sending north and the Iraqi army, with its superior, American-provided weapons was a better guarantee of safety in a volatile region than the lightly-armed Peshmerga. All that has changed now. And the referendum, originally scheduled to take place last year, is almost guaranteed to show that Iraqi Kurds are ready to break away.

All of this puts two key elements of the U.S. policy in the region on a collision course.

"The United States not only has to worry about the Islamic State, but it also needs to worry about the future unity of Iraq,” says Anthony Cordesman, a Middle East specialist at Washington’s Center for Strategic Studies.

"This is a little bit of a combination of a juggling contest and a tightrope walk,” Cordesman continued. "If you make a mistake, essentially you can trigger a new form of civil conflict."

More arms

Politicians in Washington, desperate for good news from the war against ISIS, often heap praise on the Kurds, who, with the help of U.S. advisers and close air support from the U.S. military, have managed to take back large areas that were lost to the extremists in June.

But, in an exclusive interview, the man who runs the Kurdish region’s security council told NBC News that neither airstrikes nor praise from Washington are enough to win the war.

“Praising is good. We also see ourselves as trusted allies of the United States and the free world,” Masrour Barzani, Chancellor of the Kurdistan Region Security Council, said. "But fighting needs more than just praising. It needs guns, it needs weapons."

Speaking on NBC's "Meet the Press" on Sunday, Kerry said he fully understood Barzani’s “impatience” but added: “The fact is that the Iraqi Army itself needs to be retrained and stood up."

However, the Kurds and the Iraqi Army want different things for Iraq. There is little doubt that arming the Kurds will hasten the day when the Kurds declare themselves independent. Kurdish leaders are increasingly comfortable speaking of an independent Kurdistan in northern Iraq as their goal. Independence, Barzani said, "[is] a God given right of the Kurdish people to be equal not less than any other nation on the face of the Earth.”

'Long war'

The more Kurds speak of an independent future, the less comfortable U.S. officials will likely be to send them weapons. But failing to adequately arm the Kurds would not only be a betrayal, but it could slow — or even reverse — the progress they have already made against ISIS.

“It looks like this is going to be a long war,” Barzani told NBC News. "Peshmerga armies are doing their best, fighting ISIS with whatever they have in their possession which is not much really. It’s a very difficult war."

The solution the administration has found is to split the difference, arming the Kurds just enough to fight ISIS but not with heavier weapons that could later be used in an internal war with Baghdad. The Kurds are frustrated. And so, they say, are the Americans that were sent to help them.

“Basically, they’re doing their best,” Barzani says about the American advisers. “I think many of them are just as frustrated as we are."

Balancing competing interests and goals seems like sound policy. But what seems sound on a power-point presentation in Washington does not seem reasonable to men who are fighting on the front lines. The Kurds have lost 1,000 Peshmerga in the fight against ISIS and absorbed an unprecedented wave of refugees. The patience of one of our closest allies is wearing thin.

James Novogrod of NBC News contributed to this report.