On a military base in the Mideast, the location of which is a secret, there is a giant room with more than 70 seats facing a two-story bank of television screens.

It looks like something out of “Dr. Strangelove,” but this room is the very real, everyday office of the 74-nation coalition that came together from around the world to defeat ISIS.

During battles and offensives, a representative from each country in the coalition — from Iraq to Panama, Cameroon to Croatia, Fiji to France — would take their seat in this space to monitor progress and exchange views.

Three years after the coalition was formed to fight ISIS in Syria and Iraq, 99 percent of the territory once occupied by the “caliphate” had been liberated, and 7.7 million people have been freed.

Undeniably, the multiethnic support of 74 nations in Operation Inherent Resolve helped. “The world spoke out on this,” one official told me when I tagged along with Defense Secretary Jim Mattis on a trip to Kuwait, Jordan, Egypt and Pakistan a year ago.

To the retired Marine general, the room was a tangible expression of the value of U.S. alliances in the Mideast and the wider world.

“History is clear,” Mattis said to the Senate Armed Services Committee during his confirmation hearing. “Nations with strong allies thrive, and those without them wither.”

For two years, Mattis has been a voice of reassurance to our allies as President Donald Trump pursues an “America first” foreign policy. In many cases, Mattis was able to persuade Trump of the value of those alliances, such as NATO, even though Trump thought they were taking advantage of U.S. generosity and should be abandoned or dramatically restructured.

Mattis believed that the security of the United States depended on such alliances, which the U.S. has been building since World War II. He believed creating more democratic and more stable states around the world was the key to stopping terrorism, and alliances were the best way to create those better states. He was an internationalist in a nationalist administration, in other words, and now that conflict has reached a head. Mattis is stepping down.

Mattis’ 44 years of experience as a Marine, including wars in Afghanistan and Iraq and leading U.S. Central Command in the Middle East, left him a host of deep relationships to draw on in his role as Defense secretary.

When I asked him on the plane ride over to Cairo if he had become more of a diplomat in chief than warrior in chief as Defense secretary, he answered: “No, I’ve been doing diplomacy for a long time. I’ve known a lot of these guys we’re meeting with a long time. Back when they were crown princes, I fought with some of them.”

I asked him how much it helps, having those long relationships in place in Jordan, Pakistan and other Mideast countries.

“It’s the only thing that works. Makes all the difference in the world,” Mattis said.

Mattis reiterated that faith in interdependency in his resignation letter:

“One core belief I have always held is that our strength as a nation is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships. While the US remains the indispensable nation in the free world, we cannot protect our interests or serve that role effectively without maintaining strong alliances and showing respect to those allies.”

He makes specific mention of the power of alliances after 9/11 and against ISIS.

“ … we must use all tools of American power to provide for the common defense, including providing effective leadership to our alliances. NATO’s 29 democracies demonstrated that strength in their commitment to fighting alongside us following the 9/11 attack on America. The Defeat-ISIS coalition of 74 nations is further proof.”

The room in that base in the Mideast is now mothballed and irrelevant, and Mattis will soon return to his beloved home state of Washington. And more and more, America will build up its military strength and project its might out into the world to protect our borders and promote our business relations.

As we pull back from those alliances that Mattis saw as the core of American power, the worry is that others less committed to a free and safe world will fill the vacuum, countries such as Iran and Russia and China. To see Mattis leave the administration is like watching the last vestige of the complicated world order the U.S. has presided over for 74 years float permanently away.

Let’s pray what comes next works half as well.

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