Since Moscow launched its all-out assault on Ukraine in February, Washington has vocally condemned the invasion, imposed sanctions, sent arms and other aid to Ukraine, and generally made pushing back against Vladimir Putin a strategic objective. Yet, Michael Doran explains, America’s efforts to reinstate the 2015 nuclear deal with Iran, along with its longstanding policies in Syria, only benefit the Kremlin:

It is in Syria that this contradictory approach will do the most harm. Although Russian-Iranian relations there are not perfectly harmonious, Moscow and Tehran do share a fundamental commitment to save the Assad regime and have been cooperating closely for years to achieve that aim. The hundreds of billions of dollars that the nuclear deal will channel to the Iranian regime . . . cannot but help them strengthen Assad’s grip on power.

For the United States to advance the Russian-Iranian joint project is even more striking because Syria and Ukraine are umbilically linked. In October 2015, the U.S. Navy’s top commander in Europe, Admiral Mark Ferguson, tried to raise awareness of this fact in Washington. As the Russians began their campaign to shore up Assad, Ferguson referred publicly to an “arc of steel,” by which he meant a network of new bastions of Russian naval power. The hottest segment of the arc, at that moment, was the naval bridge, stretching between the port of Sevastopol in Russian-occupied Crimea and the port of Tartus on Syria’s coast, that supplied the Russian-Iranian campaign to save Assad. But before long Putin was also using Syria as a base for extending the arc deep into the Mediterranean. In 2020, for example, Russia flew more than a dozen attack jets from Syria to Libya to support Russian forces aiding the warlord Khalifa Haftar in his effort to seize Tripoli, the capital.

In short, without the naval bridge between Sevastopol and Tartus, Russia’s capacity to project power into the Mediterranean would be circumscribed. Ukraine’s aspirations to retake Crimea, therefore, threaten Russia’s status as a Middle Eastern power—yet one more reason why Putin seeks to turn Ukraine into a satrapy of Russia. Even if Kyiv were to cede Sevastopol to Russia permanently, the rise of a fully independent Ukraine would still worry Moscow, which fears that Ukraine might build a serious navy, or might acquire surface-to-ship missile batteries and unmanned aerial vehicles capable of threatening the Russian Black Sea fleet.

When the IDF finally caught up with the late Hamas leader Yahya Sinwar, he wasn’t deep inside a subterranean lair, as many had expected, but moving around the streets the Rafah. Israeli forces had driven him out of whatever tunnel he had been hiding in and he could only get to another tunnel via the surface. Likewise, Israel hasn’t returned to fight in northern Gaza because its previous operations failed, but because of its success in forcing Hamas out of the tunnels and onto the surface, where the IDF can attack it more easily. Thus maps of the progress of the fighting show only half the story, not accounting for the simultaneous battle belowground.

At the beginning of the war, various options were floated in the press and by military and political leaders about how to deal with the problem posed by the tunnels: destroying them from the air, cutting off electricity and supplies so that they became uninhabitable, flooding them, and even creating offensive tunnels from which to burrow into them. These tactics proved impracticable or insufficient, but the IDF eventually developed methods that worked.

John Spencer, America’s leading expert on urban warfare, explains how. First, he notes the unprecedented size and complexity of the underground network, which served both a strategic and tactical purpose:

The Hamas underground network, often called the “Gaza metro,” includes between 350 and 450 miles of tunnels and bunkers at depths ranging from just beneath apartment complexes, mosques, schools, hospitals, and other civilian structures to over 200 feet underground. . . . The tunnels gave Hamas the ability to control the initiative of most battles in Gaza.

One elite unit, commanded by Brigadier-General Dan Goldfus, led the way in devising countermeasures:

General Goldfus developed a plan to enter Hamas’s tunnels without Hamas knowing his soldiers were there. . . . General Goldfus’s division headquarters refined the ability to control forces moving underground with the tempo of the surface forces. Incrementally, the division refined its tactics to the point its soldiers were conducting raids with separate brigades attacking on the surface while more than one subterranean force maneuvered on the same enemy underground. . . . They had turned tunnels from obstacles controlled by the defending enemy into maneuver corridors for the attacker.

This operational approach, Spencer explains, is “unlike that of any other military in modern history.” Later, Goldfus’s division was moved north to take on the hundreds of miles of tunnels built by Hizballah. The U.S. will have much to learn from these exploits, as China, Iran, and North Korea have all developed underground defenses of their own.