Syria may be the most complex problem on Earth. Four outside powers, Iran, Russia, Turkey and the United States, control territory or bases; others, like Israel, regularly carry out bombing raids. Even Iraq is waiting in the wings to intervene.

The war began seven years and one month ago, and despite the efforts of two international groupings dealing with Syria, the U.S.-Russian-led Geneva Process and the Astana group of regional rivals, Turkey, Iran and Russia, there’s been no end in sight. The impasse is usually blamed on the obduracy of Syrian President Bashar al Assad.

But at its heart Syria is a vast collection of war crimes masquerading as a civil war. Shortly after Syrians took to the streets in a national uprising to demand political reform in 2011, Assad went to war against his own people, targeting cities and towns, hospitals and rescue services, mosques, schools and public markets. He directed his security forces to put hundreds of thousands under starvation siege in the Damascus suburbs, blocked the population from medical supplies and repeatedly used chemical weapons, the latest case being in Douma on Saturday.

Indiscriminate bombing of civilian targets terrorized 12 million of the 23 million people of Syria into fleeing their homes, five million of them seeking refuge abroad. In the memorable phrase of Gen. Philip Breedlove, the U.S. NATO commander in 2016, Assad and his Russian backers were deliberately “weaponizing” Syrian migrants in a bid to destabilize and undermine the European Union.

Assad labeled his political opponents terrorists even as he linked up with terror groups such as the Lebanese Hezbollah, Iran’s Revolutionary Guard Corps and the Kurdistan Workers Party and ceded big swaths of territory to ISIS with hardly a fight. Now he’s turning over bases to Russia and Iran and allowing Iran to establish a land corridor to the Mediterranean.

By many estimates, more than 500,000 Syrians have been killed so far, 1,100 in Eastern Ghouta in March alone, special envoy Staffan de Mistura told the U.N. Security Council Monday. But the carnage isn’t over. The U.S. Holocaust Memorial recently warned that even greater massacres could be in the offing.

So how to untie the Gordian knot?

According to legend, Gordius, king of ancient Phrygia, which straddled the land routes to the East, hitched a wagon to a post in the eponymous town of Gordium so securely, with no ends visible, that the person who managed to untie it would be destined to rule all of Asia. In the year 333 B.C., Alexander the Great arrived at Gordium, just south of today’s Ankara, and did just that, unsheathing his sword and releasing the wagon with a single stroke.

No doubt President Donald Trump would like to find such a bold and definitive way to solve the Syrian problem. But a single military strike is unlikely to cleave Syria’s Gordian knot unless it signals a genuine shift in U.S. policy that, despite occasional flashes of fiery rhetoric, has tolerated Assad’s continued stay in power. The United States and its allies passed up numerous opportunities to curb the Syrian massacre in the past seven years, but there are still targets for attack.

The heart of the regime’s terror tactics against civilians is its Air Force. Since 2014, it has used its helicopters to drop barrel bombs—unguided containers full of explosives and shrapnel and sometimes crude chemical weapons. Its force of fixed-wing warplanes has been augmented since September 2015 by the Russian Air Force. Because relatively few young Syrian men (certainly almost none from the Sunni sect that constituted to 70 percent of the population in 2011) want to fight for the Syrian regime, it has had to rely heavily on militias organized and led by Iranian commanders. What’s tipped the military balance in the regime’s favor is its air power.

President Barack Obama had put the war in Syria on the back burner and made his top foreign policy priority in the Middle East an agreement to prevent Iran from developing nuclear weapons. By doing little to thwart Iran’s lead role on the ground or counter Russia’s air intervention, he alienated U.S. allies in the region—Arab states, Israel and Turkey—which saw the Iranian buildup as extremely dangerous. The damage done to U.S. relations in the region is unlikely to be repaired overnight, but Iran’s growing role on the ground is now seen by many, starting with Defense Secretary James Mattis, as a security threat to the entire region.

Obama’s policy also alienated many Syrians. He faulted locally based rebel factions for not having a unified leadership, but he failed to utilize the thousands of regime security sector defectors, which included officers up to senior ranks, who could have taken charge.

Instead of tapping the tens of thousands of draft-age Syrians who fled to Turkey rather than serve in Assad’s military, the Obama administration chose the People’s Protection Units, affiliated with the Kurdistan Worker’s Party, a Turkish separatist group on the U.S. list of terror organizations, to fight the ground war against ISIS. At the same time, Obama refused to arm anti-regime forces to defend the civilian population from regime airstrikes and barrel bombs.

Destroying even the helicopter force, which reportedly dropped the barrel bomb with chlorine or other gas in Douma on Saturday, would signal a change in U.S. Syria policy, for it would end the barrel bombings. But if the Syrian Air Force is allowed to continue freely targeting civilians with missiles and rockets, the impact of an American-supported intervention would be greatly lessened. Moreover, Russia could step into the breach and pick up where the Syrian Air Force left off—unless it feels its forces are at risk.

During the 10-year war in Afghanistan that began after a Russian armed intervention in 1979, the U.S. supplied Stinger Missiles to the Afghan resistance, which crippled Russia’s helicopter-borne counter-insurgency. This led not only to military defeat and a withdrawal from Afghanistan but also to the demise of the Soviet Union and a rapid end the Cold War.

The big question is whether Trump plans a single military blow or will try to leverage the use of force to achieve a political outcome. If the latter, he’ll need a plan for escalation until it is achieved. U.S. allies in the region are more likely to support the operation and its aftermath if there’s a well-thought-through plan that will end the Syrian war.

Also unknown is whether there’s a plan to mobilize public opinion. Any military intervention is bound to divide the American and international public unless it’s politically justified and fully explained, but other than Nikki Haley, the U.S. ambassador to the United Nations, no top Trump administration figure has regularly drawn attention to the war crimes of the Syrian regime and Russia.

“ Syria is a vast collection of war crimes masquerading as a civil war. ”

If the war isn’t halted, millions more civilians will remain in jeopardy. Daraa, where the Syrian revolution began in 2011, is now apparently the next target in the regime’s sights. Then there’s Idlib, a northern province swollen to a population of more than 2 million, increasing daily by residents forced out of Eastern Ghouta. Civilians in Idlib are targets almost daily of regime and Russian bombing.

There’s also the possibility that Syria will ignite a regional war. Iran’s stated goal of forging a land corridor to facilitate the delivery of arms to Hezbollah in Lebanon, coupled with plans to settle large numbers of Iranians linked with the IRGC in Syria, already is seen by Israel as a severe threat.

The horizon is bleak. The U.S. Holocaust Memorial Museum, in a report issued in mid-March, declared a “cataclysmic failure” by the International Community in Syria. It also produced an posted a series of videos, some of which are embedded here, that illustrate all too well the horrors the Assad regime has imposed on its people. “At a moment when we see an unprecedented risk of further atrocities," wrote the authors of the museum's report, "we believe that the worst might be yet to come for civilians in Syria.”