And Russia has gotten away with this partly because of the artificial line two American administrations have drawn between the civil war in Syria and the anti-ISIS campaign. But as the battle lines on the ground converge, it is no longer possible to ignore the fact that the fight against ISIS is also the fight for the future of Syria and the Middle East. Moreover, the war appears to be expanding.

As they seek to consolidate territory for the regime, Syrian, Russian, Iranian, and Hezbollah forces are coming ever closer to U.S. troops assisting Syrian Democratic Forces fighters combatting ISIS in eastern Syria. On February 7th, Russian mercenaries attacked U.S. special-operations forces near the city of Deir Ezzor. U.S. forces struck back, and body bags numbering in the double digits appear to have been transported back to Russia. This was a test of U.S. resolve by a Kremlin eager to declare victory in Syria on its terms.

The United States is on the ground in Syria with about 2,000 forces. It is part of the now-defunct UN Geneva process that had aimed to bring peace to the country. And as the death toll mounts and U.S. allies—like Israel—get sucked further into the fighting, America’s responsibility in Syria is only growing. The United States cannot sit and watch a slow-motion Rwanda unfold. We can no longer ignore the fact that our insufficient political-military action only serves to drag on a conflict that we may well be able to end.

We’ve been here before. From 1993 to 1995, the United States and its allies faced a humanitarian catastrophe in Bosnia as a result of deliberate ethnic cleansing operations directed by the government of Serbia (later adopted to a far lesser extent by all parties). For about three years, we worked to beef up the failing UN humanitarian operations and hammered away at multilateral diplomacy as body counts and refugee flows mounted.

Ultimately, only the credible threat of force stopped the suffering and the war. In 1995, the U.S. and its allies finally began bombing Serb forces attacking defenseless Muslim civilians. Serbian President Slobodan Milosevic and his Bosnian Serb allies would pay a price for attempting to seize more land by killing or forcing inhabitants to leave. Meanwhile, Croat-Bosnian forces armed and trained by the United States were repelling Serb forces from territory they had seized earlier. For Milosevic, it was time to make a deal. The result was the 1995 Dayton Accords, which have held the peace in Bosnia since then.

Military force and deterrence may also be the key to ending the Syrian war.

Russia repeatedly calls various warring parties—but not all of them—to the table and attempts to get the international community to concede that Assad will stay. Meanwhile, it continues its war of attrition in the face of insufficient resolve on the part of the United States and its allies. Without combined economic, military, and diplomatic pressure, Russia, Syria, and Iran won’t compromise. Aggressors—whether in Belgrade or in Moscow, Damascus, or Tehran—have no incentive to make concessions unless they face pressure.