America and its closest allies have built and sustained a particular kind of order since the end of World War II. Some call it a “rules-based democratic order,” others a “liberal international order.” Regardless of the label used to describe the postwar order, it’s undeniably under attack from a range of threats—powerful authoritarian states like China and Russia, revolutionary regimes like Iran, stateless groups like al Qaeda and ISIS, even “placeless” groups operating in cyberspace. Yet efforts to explain the need to defend the postwar order have been hobbled by its esoteric nature: It’s far easier, after all, for policymakers to make the case for investing American treasure and risking American lives to defend U.S. citizens, territory and interests from tangible threats like Hitler and Tojo, Stalinism and jihadism than it is to justify spending treasure and spilling blood to support the nebulous, gauzy dividends promised by the liberal international order—the free movement of people and goods, agreed-upon norms of behavior, international stability. The good news is that Joint Chiefs Chairman Gen. Mark Milley has found a way to explain, in brutally clear terms, why the liberal international order matters to the American people.

Before we get into Milley’s description of what’s at stake in the survival or collapse of the liberal international order, we should define some terms. Both “rules-based democratic order” and “liberal international order” aim to describe how America and its allies have tried to make the world work and indeed manage the world: They embraced and encouraged democratic governance; developed rules and norms of behavior; promoted liberal (freedom-oriented) political and economic institutions; and called upon governments to live up to the responsibilities of nationhood by promoting good order within and around their borders.

Although elements of this democratic order date to President Woodrow Wilson’s Fourteen Points and even earlier, this process of building a rules-based, democratic order began in earnest in August 1941, when Prime Minister Winston Churchill and President Franklin Roosevelt drafted the Atlantic Charter. Their goal was “to make known certain common principles” that would shape the postwar world: self-government, respect for borders and sovereignty, the rule of law, human dignity, an equitable peace, open markets and freedom of the seas. What came to be called the Free World built—and sustained—the postwar order on that foundation.

Outgrowths of the liberal international order include mutual-defense institutions; efforts aimed at expanding free trade and promoting human rights; and policies seeking to develop and enforce rules of the road in international relations. Thus, President Harry Truman at the beginning of the Cold War forged NATO, rescued South Korea and West Berlin from unprovoked aggression, signed on to the Universal Declaration of Human Rights, promoted GATT and other tariff-lowering initiatives, and dispatched the Seventh Fleet to prevent an invasion of Taiwan; and President Ronald Reagan at the end of the Cold War redoubled America’s commitment to NATO, reassured Taiwan, stood with Korea and Britain when they were attacked, deployed U.S. might to punish aggression and buttress international law, used the bully pulpit and economic big stick to promote human rights in the Soviet bloc, trailblazed a free trade zone spanning North America, and resolutely committed America to defend “a peaceful, prosperous and humane international order,” “strengthen a weakening international order, and restore the world's faith in peace and the rule of law.”

In short, the postwar order didn’t emerge by accident and doesn’t endure by magic. As Robert Kagan of the Brookings Institution explains, “International order is not an evolution; it is an imposition. It is the domination of one vision over others—in America's case, the domination of liberal free market principles of economics, democratic principles of politics, and a peaceful international system that supports these over other visions.” The era of “American predominance,” Kagan concludes, “has shown that there is no better recipe for great-power peace than certainty about who holds the upper hand.”

Owing partly to the fact that America set up the postwar system and partly to America’s overwhelming economic-military-industrial power after the war, America has held that upper hand since 1945. However, thanks to a confluence of factors—Washington’s drift toward disengagement, sequestration’s erosion of the Armed Forces, the public’s world-weariness, the mushrooming costs of COVID recovery programs—America is dealing away that upper hand.

For example, the U.S. defense budget has fallen from 4.7 percent of GDP in 2009 to 3.1 percent today. The Cold War average was more than twice that. This is the surest way to invite the worst of possibilities: what Churchill called “temptations to a trial of strength.” These once-avoidable trials of strength are now proliferating: with Moscow in Central Europe, Central Asia, Syria and space, with Beijing in the South China Sea, the digital domain, space, and the global supply chain, with Tehran in the Persian Gulf and Iraq, with all of these aggressor regimes in cyberspace.

If America and the rest of the Free World prove unable or unwilling to follow the example set by Churchill, FDR, Truman and Reagan, the autocrats and theocrats will replace the liberal order with something that is both less liberal (less freedom-oriented) and less orderly. Indeed, perhaps the best way to appreciate the liberal order that earlier generations built is to consider what America and the world were like before it came into existence, which brings us back to Milley’s sobering words.

“The world is entering a period of potential instability as some nations,” “terrorist groups” and “rogue actors” seek to “undermine and challenge the existing international order,” Milley explains. “They seek to weaken the system of cooperation and collective security that has been in existence for some time. The dynamic nature of today's current environment is counterbalanced by an order that was put in place 76 years ago, at the end of World War II.”

The liberal international order was put in place in 1945 because of what happened during the three decades leading up to that pivot-point year: Milley describes how the two world wars claimed 150 million human lives, how 26,000 American personnel were killed in 1918 during the Battle of Meuse-Argonne (in just 56 days), how the Axis overran most of continental Europe in less than a year, how 57,000 American personnel were killed in an eight-week span in the summer of 1944. “That is the butcher's bill of great power war,” Milley concludes. “That's what this international order that's been in existence for seven and a half decades is designed to prevent.” And that’s what the American people must grasp.

“The present order will last only as long as those who favor it and benefit from it retain the will and capacity to defend it,” Kagan observes. “Every international order in history has reflected the beliefs and interests of its strongest powers,” he explains, ominously adding, “and every international order has changed when power shifted to others with different beliefs and different interests.”

That’s exactly what’s happening, as powerful autocratic regimes work to upend and replace the existing democratic order. We will explore what a post-democratic order might look like in the next issue.