U.S.-led coalition forces hit an ammunition storage unit in northern Aleppo on September 19th. Photograph by Huseyin Nasir/Anadolu Agency/Getty

In an essay that appeared in The National Interest at the start of last year, John Mearsheimer, who is perhaps the leading academic proponent of a “realist” approach to international affairs, argued that the United States should restrict its military interventions to areas of “vital strategic interest.” He named three of them: Europe, Northeast Asia, and the Persian Gulf.

The use of the term “Persian Gulf” rather than “Middle East” was deliberate. Mearsheimer, a political scientist at the University of Chicago, believes that the U.S. government’s main interest in the region, which stretches from the eastern Mediterranean to the Arabian Sea, is insuring that “oil flows freely out of the Gulf, which in practice means preventing any single country from controlling all of that critical resource.” Based on the fact that countries such as Egypt and Syria don’t have any oil, or any aspiration to dominate the Gulf, Mearsheimer argued that what happens within their borders is of limited importance to the United States. “Given that the United States has no vital interests at stake in Egypt and Syria, let alone the capacity for fixing the problems afflicting those countries,” he wrote, “it should adopt a hands-off policy toward them.”

In dealing with the ruinous civil war in Syria, the Obama Administration hasn’t fully heeded Mearsheimer’s advice. But since 2012, when President Obama backed off his threat to attack the forces of Syrian President Bashar al-Assad if they used chemical weapons against rebels trying to overthrow Assad’s government, the United States has proceeded cautiously. Obama authorized the Pentagon to provide only small arms to those fighting Assad, and refused their requests for air cover. Even after the Islamic State established a self-styled caliphate extending from eastern Syria to northern Iraq, the U.S. military response inside Syria was largely confined to occasional bombing raids.

Obama has frequently expressed his horror at the outrages being perpetrated in Syria, and has offered sympathy for the millions of Syrian civilians trapped or displaced by the conflict. But his basic instinct has been to keep the United States from becoming more deeply involved. In a speech at the U.S. Military Academy at West Point last year, he said, “Since World War II, some of our most costly mistakes came not from our restraint but from our willingness to rush into military adventures without thinking through the consequences, without building international support and legitimacy for our action, without levelling with the American people about the sacrifices required. Tough talk often draws headlines, but war rarely conforms to slogans.”

In a post about the West Point speech, I described Obama as “a reluctant realist.” In light of the war in Iraq and the problems that the United States has faced extricating itself from Afghanistan, his adoption of the precautionary principle was perfectly understandable, and it reflected the mood of his country. Even now, with an enormous refugee crisis emanating from Syria, and with Russia having sent in men and matériel to bolster Assad’s forces, there is no popular clamor for the U.S. government to step up its involvement. To the contrary, many Americans fear getting sucked in. On Friday, when the White House announced that it was authorizing the deployment of “fewer than fifty” U.S. special-forces soldiers to assist Kurdish fighters and Syrian rebels who are combatting the Islamic State of Iraq and al-Sham, it was at pains to stress that the move does not represent a big shift in strategy.

Perhaps it doesn’t, but it does represent another acknowledgement of the limits of realism in an interconnected world, or at least the need for flexibility in applying it. Syria is indeed a small and weak country. But the civil war there, by drawing in other, stronger powers and unleashing a huge tide of refugees, has turned out to have broader ramifications.

As the civil war escalated, a number of U.S. allies—Turkey, Saudi Arabia, and some smaller Gulf monarchies—got involved in a proxy war with Iran (and now Russia) which has heightened the devastation in Syria, enabled ISIS to gain a foothold, and sharpened old enmities throughout the Middle East. Fears that the Syrian disaster will provoke a broader regional conflagration are probably overstated. (Mearsheimer is right: Syria isn’t that important.) But from London to Ankara to Riyadh to Tehran, there is a general feeling that the United States, in calling for Assad’s removal but not doing much to bring it about, created a void that other actors are seeking to fill.

The evidence of this perception lies in public statements from Saudi royals, in reports from Tehran and other Middle Eastern cities, and in reaction in Europe to Russia’s decision to intervene militarily on Assad’s side, which was widely seen as a slap in the face for the United States. Accurate or not, there is a growing perception abroad that U.S. influence is declining, and that some of the country’s traditional rivals are pushing their luck. “For the past 25 years, America has utterly dominated great-power politics,” a recent editorial in The Economist said. “Increasingly, it lives in a contested world. The new game with Russia ... that is unfolding in Syria ... is a taste of the struggle ahead.”

That proposition can be debated. What can’t be questioned is that the tide of Syrian refugees now represents a major humanitarian and political crisis for Europe, America’s closest ally. According to U.N.H.C.R., the United Nations’ refugee agency, Turkey alone has more than two million displaced Syrians on its soil. For countries like Greece, Croatia, and Slovenia, which are also being inundated with desperate migrants, the implosion of Syria represents a huge domestic challenge.

Even mighty Germany, the intended destination of many Syrian refugees, is wavering. After an initial tide of support for Angela Merkel’s decision to welcome hundreds of thousands of displaced people, many Germans are now turning against the policy, and polls suggest that support for the far right is rising. (My colleague George Packer wrote forcefully this week about America’s tepid response to the refugee crisis.) Donald Tusk, the president of the European Council, has warned that the refugee crisis threatens the cohesion of the entire European Union. “This challenge has the potential to ... cause tectonic changes in the European political landscape,” Tusk said last week. “These are not changes for the better.”

Safeguarding the stability of Europe is surely a vital U.S. interest. Indeed, there is strong realist case for regarding it as part of an extended clean-up operation made necessary when the Bush Administration decided to invade Iraq and overthrow Saddam Hussein. Ignoring the admonitions of Mearsheimer and others about the heavy costs, and unintended consequences, of military adventurism, the United States opened a Pandora’s Box. Twelve years later, Europe is still suffering the consequences.

In rethinking its “no boots on the ground” pledge and pushing a new diplomatic initiative, the Obama Administration is hopefully getting more engaged in resolving the Syrian nightmare. At this stage, anyway, that doesn’t necessarily have to involve sending in more troops. The ideal outcome would be a ceasefire between the government and rebel forces, free elections for a new government, and the construction of a united front against ISIS. A fresh round of U.N.-brokered peace talks, agreed upon by the foreign ministers of numerous countries at a meeting in Vienna on Friday, will seek to accomplish the first two of these goals.

With no agreement on the fate of Assad and Russian forces now in situ, it is hard to hold out much hope that these talks will succeed unless the United States drops its demand for regime change. Still, something must be done. Seeking to wash our hands of the problem won’t serve anyone’s interests: not those of Syria, the broader Middle East, Europe, or the United States. “America must always lead on the world stage,” Obama said at West Point. “If we don’t, no one else will.”