The battle for Mosul will soon demonstrate that the key to success is not that Washington should have surprised Daesh (ISIS) or “bombed the hell” out of it. Around 100,000 coalition forces are involved in helping liberate the city, backed by formidable American air power. They will face up to 5,000 Daesh fighters. The struggle might be bloody, but the coalition will win. The problem is, a battlefield victory could prove to be irrelevant.

When Donald Trump rails against the Obama administration for having signaled its intent to retake Mosul, he is, as usual, ill-informed. Perhaps he has in his mind a few vivid examples of surprise attacks, like the D-Day invasion at Normandy in 1944. But those are unusual cases. Nazi Germany knew that the allies were going to invade at some point, but since it occupied almost all of Europe, it couldn’t know where the invasion would take place. Britain and the United States worked hard to make the Nazis think they would land in Calais or even enter from the Balkans.

Daesh, on the other hand, controls only a handful of towns and one large city in Iraq. From the day it took Mosul, Daesh knew that the Iraqi army would try to take it back. Given the desert topography, there are only a few open paths by which to approach the city. This lack of surprise is the norm in warfare. (Think of Operation Desert Storm, when the United States slowly massed half a million troops over months to fight Iraq.) Most of the truly successful examples of surprise involve an unexpected invasion of a country – like the Nazi blitzkrieg on Poland in 1939.

The real challenge for the coalition is to ensure that in retaking Mosul, it does not set off the same sectarian dynamics that led to the city’s fall in the first place. Remember, Mosul is majority-Sunni. The reason it fell so easily in 2014 was that its residents had been misruled and abused by Iraq’s Shiite government under Prime Minister Nouri al-Maliki. As a result, when confronting a choice between Shiite militias and Daesh, they either sided with the jihadis or remained passive.

Over the past two years, Iraqi forces – often Shiite militias – have “liberated” some Sunni towns like Fallujah and then embarked on a new round of bloodletting. From the perspective of the Shiites, they are engaging in “extreme vetting” to ensure that Daesh sympathizers are weeded out. But Sunni residents feel they are being rounded up, presumed guilty, and denied entry back into their homes and neighborhoods.

The root cause for the rise of Daesh in Iraq and Syria is political – the discontent of Sunnis in the region who see themselves as ruled by two anti-Sunni regimes in Baghdad and Damascus. Some of this is the resentment of a population that believes it should be in power, some of it a response to genuine persecution. In any event, without addressing the discontent, Daesh will never stay defeated.

When Mosul fell, many experts, including within the Obama administration, wanted Washington to rush to the aid of the Iraq government. But President Obama resisted these calls because he understood that the underlying problem was sectarian. He insisted that the Iraqi government fundamentally change its attitude toward the Sunnis – in effect, demanding that Maliki resign. Only when that happened and a new, more conciliatory leader emerged did America agree to militarily support the Baghdad government.

Every country wants a free ride. Most governments would be happy if the United States would fight their battles for them with no strings attached. In the Arab world in particular, this disease is widespread. Coalitions signed on to fight in Syria but – with a few exceptions – very quickly become inactive, leaving all the heavy lifting to America. Some argue that the answer is to publicly shame and harangue allies. That hasn’t worked in the past and is unlikely to in the future. The only strategy that seems effective is for Washington to signal that it will not pick up the slack – and mean it. It was only when it became clear that the Obama administration really would not help Iraq unless the government changed course that Maliki resigned.

This strategy of forcing others to take action was once described by an Obama official as “leading from behind,” and while the phrase is unfortunate, the idea is exactly right. In this case, it is only the Arabs who can address the sectarian dynamic by engaging in genuine reconciliation and power-sharing. The United States can help in this process, but only if these countries and their leaders actually want to help themselves.