Co-authored by W. Robert Pearson, former U.S. ambassador to Turkey. This article first appeared on The Huffington Post.

Among the images from Wednesday's carnage in the suburbs of Damascus are scenes of children's bodies laid out on floors. One rescuer described finding entire families in their homes. "They were lying where they had been. They looked like they were asleep. But they were dead," he said. While there is ambiguity about whether the scores, if not hundreds, of deaths were caused by chemical weapons, the fact remains that the Assad government carried out these atrocities against its own people -- and has been carrying out callous killings for more than two years.

The situation is indeed grim, with more than 100,000 Syrian casualties -- many of them civilian, as in Wednesday's attack -- and an international refugee crisis, with more than 1.5 million Syrian refugees registered in neighboring countries and an estimated 4.25 million Syrians internally displaced.

The atrocities must receive a response, and that response must be effective military action against Assad by the United States. Hitting Syrian armed forces most capable of producing mass casualties among civilians and the opposition is an action within our capability. Strikes against Syrian air forces or key installations has already proven to be possible. Our action should be accompanied with a clear message of deterrence that repeated chemical weapons use would trigger a larger response. 

Though the failure by the United States to act militarily on grave international crises has proven to produce dire consequences again and again -- such as in the Balkans prior to the NATO intervention and in Rwanda in 1994 -- up to this week, the mood in the U.S. government has been against intervention in Syria. For example, in a letter to Representative Eliot Engel (D-NY) dated August 19, General Martin Dempsey, chair of the Joint Chiefs of Staff and Obama's chief military advisor, argued that because Syria's rebels do not support American interests military action is unwise.

Military action, however, by hastening the fall of a tyrannical regime, shores up American interests by telling the Arab world that the United States is fully committed to positive change in the region. Effective action would restore hope to millions of Arabs who wanted fundamental change in 2010 and 2011. 

At the moment, while the United States makes moves such as canceling joint U.S.-Egyptian military operations to signal its displeasure with the Egyptian Army's killing of citizens, it glosses over the fact that the Syrian regime has been doing just that since 2011, with no letup in sight.

The situation is all the more dangerous given the regional aspect of the conflict. If the northwest Middle East -- Iraq, Syria, Lebanon, Israel, and Turkey -- is stable, the gradual realization of the democratic promise of the "Arab Awakening" is much more likely. History shows repeatedly that internal conflicts spread beyond borders if not contained. In this vital region, Lebanon is already further destabilized, Jordan is under growing threat, Iraq is being drawn into the conflict along sectarian lines, Iran is providing financial and military assistance to Assad, tensions within Turkey are rising and Russia is all but allied with the Syrian state. U.S. inaction may already have added to this instability by creating a vacuum being filled by al Qaeda affiliates, though we hear that very fact now being used as a basis for continuing to stand aside. 

A clear demonstration of American principle and will is thus required -- and now. Are we to wait while attacks become more frequent, while more extremists fill the ranks of the opposition, while fragile neighbors become more stressed, and while de facto allies of Assad are encouraged? The stage in this conflict has been reached in which continued inaction by the United States highlights our strained definition of national security interests and becomes a factor used by Assad to feel secure enough to carry out ever more horrifying atrocities.

The Syrian people deserve better than they are receiving at the hands of the West. Striking now would be a forceful sign that America still stands for principle in the world and will act on it. "All that is necessary for the triumph of evil is that good men do nothing," Edmund Burke reminded us. Will we continue to sit on our hands and let this happen, or will we do the right thing?

W. Robert Pearson is a former U.S. ambassador to Turkey. Wendy J. Chamberlin is a former U.S. ambassador to Pakistan.