Opinion | The Islamic State Has Not Been Defeated

Thus, notwithstanding the catastrophic military blows the group has suffered and the loss of its territorial rule, the Islamic State has made it unmistakably clear that it will carry on the fight even if the caliphate is militarily incapacitated. In early March, Islamic State fighters released a video from the Syrian town of Baghuz that urged the group’s followers to maintain their faith in the caliphate, even as Kurdish forces advanced toward the last of its territory.

Unfortunately, it appears that the Islamic State has both the will and limited assets necessary to survive to fight another day.

Indeed, before he was killed by an American airstrike in Syria in 2016, Abu Mohammed al-Adnani, the Islamic State’s second most powerful leader, after Abu Bakr al-Baghdadi, prepared followers for the future battles. He said, referring to the group’s progenitor, Al Qaeda in Iraq: “Do you, O America consider defeat to be the loss of a city or the loss of land? Were we defeated when we lost the cities in Iraq and were in the desert without any city or land?”

Like Al Qaeda in Iraq, which was declared “defeated” from 2006 until 2010, the Islamic State is returning to its insurgent roots. And less than a year after its expulsion from major urban centers, the organization now wages a low-intensity guerrilla campaign that has already killed hundreds of Iraqis, including key security personnel and tribal leaders. Designed to terrorize local communities, sow instability and expose the impotency of Iraq’s security forces, the Islamic State’s strategy is paying dividends.

The corrupt and dysfunctional Baghdad government has neglected the emaciated Sunni-inhabited cities (such as Mosul) that were liberated from the Islamic State’s rule. Once again, the extremist organization is appealing to disgruntled Sunnis who feel forsaken by the Shiite-dominated authorities. The recent intensification of the United States’ rivalry with Iran in Iraq under President Trump has served to only further weaken the central government in Baghdad and embolden the Islamic State.

Similarly, in Syria, sleeper cells frequently attack the liberated Raqqa and Deir Ezzor province and inflict heavy casualties on the Syrian Democratic Forces, an American-backed coalition of Kurdish and Arab fighters. Like in Iraq, the Islamic State bides its time in Syria, hoping that Turkey’s fixation with the Kurds and Mr. Trump’s decision to ultimately withdraw most American troops from the northeast will create a security void that it can fill.

Before Mr. Trump takes a victory lap, he should know that the next phase of the struggle against the Islamic State and Al Qaeda will be complex, costly and prolonged. A counterterrorism strategy is not sufficient. Permanently defeating these jihadist groups will require an economic, political and ideological strategy with a long-term focus.