Earlier this week, Mosul—the largest city under Islamic State’s control—fell to Iraqi forces, while Islamic State has been driven almost entirely from its capital of Raqqa in Syria. Reports even circulated yesterday that the caliph, Abu Bakr al-Baghdadi, had been killed. With Islamic State (IS) poised to fall, Elliott Abrams explains what’s next for the U.S.

The defeat of Islamic State as a “state” will leave two serious questions facing the United States. The first is: who will fill the spaces from which the jihadist group is driven? There is a clear effort by the new Iran-Hizballah-Shiite militia-Russia coalition to reply: “We will.”

That is an answer the United States should reject. Such a development would cement an anti-American coalition in place, threaten Jordan and Israel, and leave Iran the dominant power in much of the region. To reject this challenge verbally would be a joke, however; it must be resisted on the ground, through the use of force by a coalition that must be built and led by the United States. . . .

[O]ne can envision a discussion with Russia of how our interests and theirs can be accommodated while bringing the violence down to a level that allows many refugees to return home. But that discussion will achieve nothing unless American power first gains Russian respect and the Russians come to realize that compromise is necessary.

Even in the best-case scenario, with IS defeated and losing its control over a “state,” it may continue to exist as a terrorist group—and in any event al-Qaeda and other jihadist groups will not disappear. . . . So long as Iran tries to dominate the entire region and Sunni jihadist groups target the United States, the defeat of the Islamic State changes—but does not diminish—America’s stake in Middle East power politics.

On Tuesday, a Hizballah drone attack injured three people in northern Israel. The next day, another attack, targeting an IDF base, injured eighteen people, six of them seriously, in Arab al-Amshe, also in the north. This second attack involved the simultaneous use of drones carrying explosives and guided antitank missiles. In both cases, the defensive systems that performed so successfully last weekend failed to stop the drones and missiles. Ron Ben-Yishai has a straightforward explanation as to why: the Lebanon-backed terrorist group is getting better at evading Israel defenses. He explains the three basis systems used to pilot these unmanned aircraft, and their practical effects:

These systems allow drones to act similarly to fighter jets, using “dead zones”—areas not visible to radar or other optical detection—to approach targets. They fly low initially, then ascend just before crashing and detonating on the target. The terrain of southern Lebanon is particularly conducive to such attacks.

But this requires skills that the terror group has honed over months of fighting against Israel. The latest attacks involved a large drone capable of carrying over 50 kg (110 lbs.) of explosives. The terrorists have likely analyzed Israel’s alert and interception systems, recognizing that shooting down their drones requires early detection to allow sufficient time for launching interceptors.

The IDF tries to detect any incoming drones on its radar, as it had done prior to the war. Despite Hizballah’s learning curve, the IDF’s technological edge offers an advantage. However, the military must recognize that any measure it takes is quickly observed and analyzed, and even the most effective defenses can be incomplete. The terrain near the Lebanon-Israel border continues to pose a challenge, necessitating technological solutions and significant financial investment.