The battle to retake the Iraqi city of Fallujah has begun: 20,000 Iraqi soldiers, backed by US air power and advisers, are attempting to expel some 800 to 1,000 ISIS fighters.

This is now the third time since 2003 that US and Iraqi forces have fought to retake Fallujah (building on an even longer British tradition of retaking Fallujah.)

But the question is not whether the US and its allies will win in Fallujah — they always do. The real question is whether it will finally matter. As the latest battle for Fallujah commences, the taking and retaking of the city has become a symbol of the utter pointlessness of US efforts in Iraq.

Fallujah is costly to retake, but the US is always successful

The strategic value of Fallujah is clear. It's only about 40 miles outside of Baghdad along the Euphrates River and controls the main highway to Jordan and Syria. The presence of ISIS there is a constant threat to Baghdad and a thorn in the side of the Iraqi government. ISIS must be rooted out of Fallujah before the Iraqi military can turn its attention to the bigger prize of Mosul, Iraq’s second city, in the north.

Yet the price of the battles of Fallujah has been very high for all involved. The second battle of Fallujah in 2004 was the bloodiest of the 2003 to 2011 Iraq War. The US lost nearly 100 soldiers there in retaking the city in 2004. The insurgents lost as many as 1,500.

The city has been reduced to rubble several times, and virtually all of the city’s occupants— about 350,000 people — have been forced to flee their homes over and over again. Many more people will die in the next battle, as ISIS defends the city fiercely and leaves behind a sea of booby traps.

Still, the US and its allies have won all of their previous battles for Fallujah. And although the US will only be playing a supporting role this time around, it should be successful as well. The US military is an incredibly effective learning organization and every time it retakes the city of Fallujah, it gets better at it.

But retaking Fallujah is only the first step

The problem is what happens once ISIS is gone and the Iraqi government takes over. In 2013, the city's Sunni residents revolted against the central government in Baghdad because of its sectarian oppression. From their perspective, the Iraqi government under Prime Minister Nouri al-Maliki had begun a systematic oppression of the Sunnis, focused on purging the security forces of Sunnis and arresting leading Sunni politicians.

Today, there is a new, gentler government in Baghdad. It is financially and militarily weak and has made encouraging moves toward decentralization of power and reconciliation with the Sunnis and Kurds. But is still dominated by Shia, it still relies on fiercely sectarian Shia militias for its military strength, and it has failed to achieve any sort of reconciliation with Iraq’s Sunnis.

Without any progress on reconciliation, the Sunnis and Shia in Iraq will continue to see each other at existential enemies. The Iraqi central government, which depends on Iran and various Shia militia for its survival, will not drift naturally toward an inclusive policy.

Indeed, as the Iraqi central government recovers its strength on the back of loans from international financial institutions and US military support, it will likely return to its old efforts at repression. ISIS, as it loses territory, is cooperating in this evolution by resorting to its old strategy of reinforcing the sectarian dynamic in Iraq through a campaign of bombings in Baghdad.

Already, protesters in Baghdad, spurred on by more radical Shia elements, are demanding better security and an end to government corruption, and putting pressure on the government to crack down on the Sunni extremists. It is very easy to see this dynamic spinning out of control once again, and pushing the Sunnis in Fallujah and Iraq generally back into the hands of the next group of extremists (or just ISIS 3.0 — the extremists also tend to repeat themselves in Iraq).

Fallujah is symbolic of the broader flaw in the US strategy in Iraq

Many US officials and analysts believe that Iraq descended into sectarian strife because the US withdrew too early in December 2011. Iraq was still fragile and its communities still unreconciled, so it quickly descended into sectarian chaos once US troops left. This culminated in the ISIS invasion in 2014.

To get it right this time, these same officials and analysts proclaim, the US has to stick it out in Iraq: staying in force, overseeing the Iraqi government, and tamping down sectarian tension until the Iraqi polity is fully matured. How long will this take? John McCain thinks maybe 100 years.

There are, unfortunately, a few problems with this plan.

First, it remains remarkably unclear how just a few thousand troops (there are currently about 4,000 to 5,000 US forces in Iraq) would be able to exercise that kind of influence in Iraq. Currently, US views are important to the Shia power brokers in Iraq because US assistance is necessary to train Iraqi forces and retake ISIS territory — and yet the US has still been unable to push the Iraqi government very far toward sharing power or achieving reconciliation.

Once ISIS is kicked out of the cities, though, the US will lose what little leverage it does have with the Iraqi government. What precisely will US forces do then to stop Shia oppression of the Sunnis or end corruption in the Iraqi government?

The only real way US forces could truly exercise that level of control over the Iraqi government is through an occupation. Experience implies that the Iraqis will not accept that level of interference in their affairs for anything close to a century.

Indeed, on the question of US ground troops, Iraqi Prime Minister Haider al-Abadi, whom the US helped put into power in 2014, unequivocally declared: "We don’t want them. We won’t allow them. Full Stop." Elsewhere, he stated: "Any foreign ground troops on Iraqi soil will be treated as enemy troops." This does not sound like a recipe for a long-term, peaceful stationing of forces.

Moreover, is it truly realistic to believe that the US public, and future US presidents, will accept a 100-year occupation of Iraq? McCain points out that the US public has accepted precisely that in Germany, Japan, and South Korea.

But except for the brief period immediately after World War II in Japan and Germany, those have not been occupations. The forces were simply stationed there at the request of the government — they played no role in governance and did not get involved in domestic politics. They live a very peaceful existence.

McCain and others, in contrast, are asking US forces in Iraq to exercise 100 years of coercion in Iraq. As McCain himself noted, if US troops in Iraq continue fighting and dying, even in small numbers, the US public will tire of the exercise. At some point in the coming decades (and probably sooner), a future president will offer the US public a way out, much as Obama did in 2011.

At that point, Sen. McCain, seeking reelection for his umpteenth term in the Senate at the tender age of 97, will declare the entire effort to have been wasted and predict that Iraq will fall back into chaos without a reinsertion of US forces.

If that happens, though, don't worry: The US military will just retake Fallujah. They are very good at it.