These videos, like Mr. Adnani’s speech and articles about inhiyaz, are meant to prepare Islamic State fighters for the loss of territory. But the United States and its allies should pay attention, too.

For the Islamic State, Wilayat al-Furat is no less important than Mosul. For long-term survival, the desert matters as much as the cities. Wilayat al-Furat is the only province that crosses the Iraq-Syria border and the territory and remote areas like it are potential hide-outs for senior members — if they are not there already.

Iraqi officials already see signs of what the Islamic State’s retreat into the desert could mean. Two security officials in Salah ad Din, a province north of Baghdad, said in a recent TV interview that the Islamic State was returning to areas liberated since December 2014, recruiting new members and organizing hit-and-run and suicide attacks in populated areas. As in Egypt’s Sinai Peninsula and Pakistan’s rural northwest, overstretched security forces are not able to keep up.

As the Islamic State’s leaders remember, this is what happened after 2007. The desert became a base, mostly for foreign fighters, while Iraqis stayed behind. The group’s presence in rural areas also allowed the group to replenish their coffers with highway robbery and extortion. The militants focused their attacks on the tribal adversaries and Iraqi security forces, sowing distrust and fear, making conditions ripe for their return six years later.

But this time conditions are even more conducive to the Islamic State’s rebuilding. Iraq now is more politically and socially fractured than it was then. And, as one Iraqi who participated in the Awakening Councils told me, there is now no Sunni group in Iraq that can fill the void left by the Islamic State. The conflict in Syria further complicates the situation: Even if the Islamic State is driven from populated areas in both countries, the open desert border between them will make the group hard to chase.

The war against the Islamic State is unwinnable without filling the political and security vacuum that now exists in too much of Iraq. The Islamic State’s eventual retreat from Mosul will be a much-needed victory for the country. But unless the government in Baghdad enables Iraqi Sunnis to fill that void, it will once again emerge from the desert.