To revisit the U.N.’s anointing of Aleppo as a World Heritage Site is a haunting exercise. The U.N. celebrated the city’s “13th-century citadel, 12th-century Great Mosque and various 17th-century madrasas, palaces, caravanserais and hammams,” all of which constituted “the city’s cohesive, unique urban fabric.” This Aleppo, after five years of brutal war, is a place now dead and buried.

Since 2011, around 470,000 Syrians have died, and life expectancy in the country has fallen from 70 to 56. Meanwhile, over 11 million Syrians—roughly equivalent to the entire population of Ohio—are either internally displaced or have fled the country entirely, in one of the biggest exoduses in modern history.

The war has turned ordinary Syrians into flotsam and jetsam, lost amid national forces beyond their control, including the brutal dictator Bashar al-Assad, extremist groups such as the Islamic State, and regional actors like Iran, Hezbollah, Turkey, Saudi Arabia, and Russia. But if the civilians were hoping for Western action to stop the bleeding, they have fallen prey to another set of dynamics they can’t govern or even necessarily understand. Historically, Washington’s zeal for intervention in humanitarian crises follows a cycle. And the Syrians, unfortunately, are dying during the wrong phase.

At the start of the cycle, Washington feels compelled to act by a mixture of moral concerns and security interests. The subsequent intervention is often branded as a failure. A negative “syndrome” emerges, and Americans say “never again.” During the next emergency, the United States stands aside and civilians are slaughtered. Memories of the failed military intervention recede, guilt sets in, new security interests emerge, the U.S. cavalry gathers once more on the horizon—and the cycle begins anew. Throughout the process, people focus almost exclusively on the last big debacle, whether it was a failure of action, or a failure of inaction.

The cycle began after the end of the Cold War, when the international community rallied to eject Iraqi forces from Kuwait in the Gulf War. Then, there was a brief period of optimism about building what President George H. W. Bush called a “new world order,” based on the rule of law, that would ensure global peace, security, and freedom. U.S. forces subsequently contributed to humanitarian interventions in northern Iraq in 1991 and Somalia in 1992. But the mission in Somalia unraveled after 18 U.S. soldiers died in the “Black Hawk Down” battle in Mogadishu in October 1993. The cycle turned, and Americans grew wary of foreign wars. The Somalia syndrome stymied U.S. action in Bosnia, and helped to prevent any effort to stop the Rwandan genocide in 1994. But over time, guilt about the “lessons of Bosnia” and the “lessons of Rwanda” encouraged a new phase of interventionism in Kosovo in 1999. After 9/11, the global war on terror dramatically energized the willingness to use force. Of course, security interests came first, and humanitarianism a distant second. But the new wave of interventionism crashed against the rocks of Iraq and Afghanistan, and the Iraq syndrome produced a profound anti-interventionist mood for much of the past decade.

Critically, the tragedy in Syria began in the spring of 2011, at the extreme non-interventionist point of the cycle. Then, the United States was withdrawing its combat forces from Iraq, and would soon begin drawing down its troops in Afghanistan. While the United States did join the international humanitarian intervention in Libya in 2011, it “led from behind,” employing air power and rejecting the use of ground troops out of hand. Americans had almost zero appetite for more nation-building or further embroilment in foreign civil wars: In November 2011, approval for the war in Iraq hit an all-time low of 29 percent.

Obama’s perceptions of the Syrian civil war reflected the non-interventionist phase of the cycle. In his prominent piece in The Atlantic on Obama’s foreign policy, Jeffrey Goldberg concluded: “Syria, for Obama, represented a slope potentially as slippery as Iraq.” Obama admitted that if there had been no wars in Iraq, Afghanistan, or Libya, he might have taken more risks in Syria. “[A]ny thoughtful president would hesitate about making a renewed commitment in the exact same region of the world with some of the exact same dynamics and the same probability of an unsatisfactory outcome.”

Syrians hoping for Western support were not just fighting the regime in Damascus; they were also fighting the swiftly turning wheel of fate. Consider: If a conflict like the Syrian Civil War had broken out in 1991 or 1992, Washington might have intervened to protect the new world order laid down by Bush and sustained under Clinton. But if the conflict had begun two years later, the odds of a U.S. operation would have fallen because of events thousands of miles away in Somalia. If we delay our hypothetical Syrian conflict a few more years to the late 1990s, guilt over Rwanda or Bosnia could have boosted calls for action. By chance, the conflict occurred in 2011: a moment when the odds of Washington coming to the rescue were at the lowest point in a generation.

It’s far from certain, of course, that a more muscular American intervention would have served U.S. interests, or even helped the Syrian people. The myriad factions in the civil war, the rise of ISIS, and the internationalized nature of the conflict, make it difficult to identify exactly when and how U.S. intervention could have decisively—and positively—shaped the fighting. At the same time, it’s hard to imagine how things could have been worse for the local people with greater Western commitment. Syria is racing along an arc that bends toward chaos.

The odds of effective American action were shaped less by the extent of Syrian suffering, and more by the arbitrariness of timing. Syrian civilians have no sway over the cycle, but their survival may, nevertheless, hinge on the turn of the wheel. Eventually, the cycle will shift again. Memories of the Iraq War will fade. Guilt over the failure to act in Syria may deepen. Emerging national-security threats could encourage a new era of interventionism. And presidents, while constrained by the popular mood, also have the capacity to slow or accelerate the cycle. A future president may well oversee a more muscular foreign policy. When the next humanitarian crisis occurs, the cry of “no more Aleppos” may be compelling. In that sense, at least, Syrian civilians won’t have died entirely in vain.