Displaced Christians, who fled violence in Mosul, wait before receiving medicines during a distribution organized by the city’s Health Department at Mar Afram Church of Chaldean Catholics on August 24, 2014 in the southern port city of Basra. Agence France-Presse/Getty Images

When I attended Stanford in the 1990s, explaining my ethnic background to fellow students was a challenge. I am Chaldean. Or as my more scripted response became: “We are ethnic Assyrians from northern Iraq who belong to the Chaldean Rite of the Catholic Church.”

I would explain how Chaldeans are members of the Eastern Catholic Church, while Assyrians are members of the Assyrian Church of the East, independent of the Roman Catholic Church. Both, however, share a common ethnic heritage distinct and apart from their Arab neighbors in Iraq. We speak a colloquial form of Aramaic, the same language spoken in the Mideast at the time of Christ.

Having heard of ancient Assyrian civilization at some point, many responded with: “They still exist?” Feeling a bit like a museum artifact, my answer at the time was a simple: “Yeah, we exist.” Today, as the Islamic State of Iraq and al-Sham continues its rampage through northern Syria and Iraq, I would add: “for now.”

Before the U.S.-led invasion of Iraq in 2003, an estimated 1.4 million Chaldeans and Assyrians inhabited Iraq. In the decade that followed, hundreds of thousands of these Iraqi Christians either sought permanent refuge abroad or were internally displaced. During this turmoil, more than 60 churches were bombed, a Chaldean Catholic Archbishop was kidnapped and murdered, and an Iraqi Christian population of 1.4 million dwindled to fewer than 500,000—a result of the insurgency, subsequent unrest, and radically anti-Christian sentiment that ensued.

By no means are today’s Iraqi Christians novices at living among conflict. For more than 2,000 years, Chaldeans and Assyrians survived countless Persian wars, persecution as early Christian converts, Mongol siege, Arab conquest, Ottoman subjugation, Western colonial rule, postcolonial coups, war with Iran, the Arab-Kurd conflict and chemical-weapon attacks.

Today, targeted by ISIS for their Christian faith, Chaldeans and Assyrians are the victims of an unabashed ethnic-cleansing campaign. After seizing the northern city of Mosul in June, ISIS spray-painted the symbol for “Nazarene” on the homes of Christians. Families had 24 hours to convert to Islam, leave the city or face execution. Christians leaving the city had their possessions confiscated at security checkpoints and were forced to leave with nothing.

Most refugees fled to neighboring villages under the protection of Kurdish security forces, the Peshmerga. In response, ISIS shut off water supplies from Mosul to those villages. ISIS then continued its rapid advance into the villages outside of Mosul, displacing hundreds of thousands from their homes, converting churches to mosques, destroying homes and businesses, and leaving nothing to return to. An entire people have been cleansed from the region, guilty of nothing but their faith and ancient ethnicity.

While recent U.S. airstrikes have helped, the Obama administration appears to be pursuing a policy of containment, combined with a naïve hope that the ISIS threat will somehow dissipate. Whether efforts to rally our NATO allies and neighboring Middle East states to help Baghdad and the Kurds defeat ISIS remains to be seen.

What is clear is that the fate of Chaldeans and Assyrians in northern Iraq remains exclusively in the hands of outsiders. Having weathered endless storms of unrest in the region for thousands of years, the biggest threat to their continued existence today is silence and the unwillingness of Western leaders to acknowledge a genocide in the making.

I was the executive director of the Chaldean Assyrian Syriac Council of America from 2008-10 and my primary task was to communicate the plight of Iraqi Christian minorities to the U.S. government. Our council was successful in initiating and passing nonbinding Senate Resolution 322 (2010) and House Resolution 944 (2010), each calling on the Obama administration to work toward ending the marginalization and persecution of ethnic minorities within Iraq. But most of our calls for actual assistance fell on deaf ears.

Some officials expressed concern that U.S. support for Iraqi minorities—Christians in particular—could tarnish relations with the Arab world by suggesting favoritism toward Western religion. Other officials insisted that Iraqi minorities use “democratic” channels within Iraq to address their concerns.

Such channels have all but dried up, if they ever existed. It was once thought that the “rising tide” of democracy in Iraq would, over time, alleviate the plight of Iraqi minorities. What ISIS has taught us in recent months is that if there is a rising tide in Iraq, it isn’t democracy. As for the future of Chaldeans and Assyrians, at least I can confirm that we still exist—for now.

Mr. Kuriakuz is a former executive director of the Chaldean Assyrian Syriac Council of America.