In the wake of yet another chemical weapons attack in Syria, the world looks on in horror but not surprise. Crimes against humanity have become routine under the government of President Bashar al-Assad. On April 14, the United States, Great Britain and France retaliated for this latest outrage with missile strikes against three chemical weapons storage and research facilities in Syria. This was a welcome decision by President Trump, but without a consistent strategy the strikes mean little. Absent further pressure on the Assad regime, there is no end in sight to the slaughter in Syria, both from chemical weapons and from the heavy bombing of civilian areas.

The Compendium of the Social Doctrine of the Church makes clear that all governments have a responsibility to “ensure that the conditions of peace exist, not only within their own territory but throughout the world.” Backed by Russia and Iran, the Assad regime currently has nothing to lose and much to gain from continuing its war on Syrian citizens. The conditions for peace will not exist until this reality changes, and a one-time strike will not be enough.

The United States, as the world’s most powerful country, has a moral responsibility to protect the innocent and to ensure some semblance of justice in international affairs. It is time for the strong and powerful to stand up for the weak, the innocent and the vulnerable. It should go without saying that the United States should avoid further casualties among the Syrian civilians in opposition-held areas who have been subject to indiscriminate killing for years. However, attacking the military assets of the Assad regime is justifiable.

When the Assad regime launched a sarin-gas attack in 2013, killing hundreds outside of Damascus, it crossed President Obama’s now-infamous “red line” warning against the use of chemical weapons. Instead of a military response, the United States reached with Russia in 2013 to eliminate Syria’s chemical weapons stockpile, a diplomatic move that has clearly failed. The most effective way to ensure that these weapons are not deployed again would be to destroy the means by which they are delivered.

The United States has a moral responsibility to protect the innocent and to ensure some semblance of justice in international affairs.

Whether military action meets the conditions of “just war” under the teachings of the Catholic Church requires, among other things, a high probability of success and its being a act of last resort. But the fact is, beyond the largely symbolic strikes in 2017 and now one in 2018, the United States has not placed significant military pressure on the Assad regime. While the prospect of success is by no means certain, a more assertive strategy is almost certain to have a better result than continuing to issue routine condemnations of crimes against humanity from an ocean away.

As for the question of last resort, all realistic peaceful options have been exhausted. There are no new ideas for how to put pressure on Syria or Mr. Assad’s Russian and Iranian backers, who are already subject to significant sanctions. The Syrian government has conducted repeated “talks” with domestic opposition forces, but Mr. Assad has used those negotiations as a stalling tactic, while continuing to launch military offensives that kill thousands and displace tens of thousands more. Russia insists that its ally is not responsible for chemical weapon attacks, but, tellingly, it has vetoed attempts by the United Nations to investigate the use of chemical weapons in Syria nine times. As long as this continues, why would Mr. Assad negotiate?

A more assertive strategy is almost certain to have a better result than continuing to issue routine condemnations of Mr. Assad from an ocean away.

In order to create the conditions for a lasting peace, the United States and its allies must cripple Mr. Assad’s ability to wage war. Every effort must be made to avoid civilian losses, but innocent blood is already being shed in Syria as a result of American inaction. The United States has not had a stellar military history in the Middle East, but U.S. air strikes have stopped senseless killing before, notably in the Balkans during the 1990s.

There are also peaceful options to help the Syrian people, but they are not exclusive of military action. For example, it is unconscionable that President Trump refuses to welcome Syrian refugees into the United States. We should conduct a Syrian resettlement effort comparable in scale to the resettling of refugees at the end of the Vietnam War. Yet it is also unconscionable to refuse to do anything about that the dictatorship that has forced so many to flee in the first place.

We must welcome Syrian refugees, but it is unconscionable to refuse to do anything about that the crimes against humanity that have forced so many to flee.

It was a Syrian refugee who first convinced me of the need for U.S. military intervention in Syria. In October 2015, I was on the Greek island of Kos, documenting the refugee crisis that had by then spilled onto European shores. I met dozens of Syrians, mostly from Aleppo and Idlib. The month before, the Russians had intervened in the Syrian civil war. I had the opportunity to hear from refugees firsthand, and I asked them about their journeys, their hopes for reaching Germany and their feelings about the xenophobia against them already spreading in the West. But they mostly asked me one thing: “Why don’t you Americans do anything about Assad?” I had no answer to their question.

I know many people who oppose intervention. They fear spiraling violence and are wary after the experiences of U.S. intervention in Iraq and Afghanistan. They do not believe violence can be the solution to violence. But the repeated use of chemical weapons against civilian populations indicates that Mr. Assad and his allies have no moral qualms about the use of force. Violence is indeed proving an effective solution to Mr. Assad’s problems. The use of chemical weapons is helping him win, and if he wins, Mr. Assad and others will have learned they can get away with it.

There is also an understandable fear that U.S. intervention could spark a global war, given Russian and Iranian involvement and especially in light of President Trump’s belligerent and unsettling tweets. But while Mr. Trump’s temperament is cause for worry, waiting for a new presidential administration before taking action would condemn thousands more to slaughter. And while we should not target Russian forces directly, the U.S. military has struck Russian forces in Syria before without provoking a backlash.

If we have learned anything from the past seven years of the Syrian conflict, it is that Mr. Assad cannot be shamed into respecting human rights or civilian life. Last week, another several hundred Syrian civilians paid the price for our inaction. I fear that after our brief military strike, we will once again move on. If the United States does not continue to apply constant military pressure on the forces of Bashar al-Assad, the lesson to every dictator and war criminal will be that they can get away with any atrocity if it works to keep them in power. And we must seek more than simply restraining the use of chemical weapons; after all, does a death by barrel bomb truly trouble us so much less than death by chlorine gas?

In order to give diplomacy a chance and address the root cause of the refugee crisis, Mr. Assad needs to understand that victory by his current brutal and illegal methods is not possible. Let us emulate the clarity of the students of Parkland, Fla., and say: “No more thoughts, no more prayers, we need action.”

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Antonio De Loera-Brust is the communications director for the United Farm Workers. He previously served as special assistant to U.S. Secretary of State Antony Blinken. He was an O’Hare fellow at America Media from 2017 to 2018.