Gabriel Glickman is an adjunct professor of history and is currently writing a world history book provisionally titled, “The Rise and Fall of World History: Avoiding Historical Amnesia in 21st Century Classrooms.”

President Trump says his new national security strategy puts “America First.” (Evan Vucci/AP)

The Trump administration’s National Security Strategy (NSS), released Monday, puts “America First.” In other words, there is no chance this Republican administration will share the moral imperative of the last Republican administration, led by George W. Bush, that emphasized the maintenance and expansion of a liberal world order.

Indeed, the opening statement of the 2002 Bush NSS reads the opposite of President Trump’s: “The United States must defend liberty and justice because these principles are right and true for all people everywhere.” Trump’s NSS states: “Putting America first is . . . the foundation for U.S. leadership in the world.” In other words, U.S. leadership in the world is a secondary factor in Trump’s foreign policy outline.

Most administrations do not strictly adhere to their NSS. As pointed out by historian Max Boot, the Trump administration’s NSS appears to be an amalgamation of the competing ideologies within the White House more than a definitive philosophy of the president himself. Still, given the stakes of abandoning the liberal world order, it is important to understand what exactly it is, and what America’s role in maintaining it has been. Only then can we grasp the serious ramifications of the Trump administration potentially walking away from it.

Let’s start with the “liberal” part of the liberal world order. Liberalism here does not refer to free sex, legalized marijuana or other social trends that have become part of the platform of modern liberals. Instead, it refers to the liberalism that emerged from the French Revolution. Loosely defined, these first liberals — classical liberals — believed in transparent, accountable government and free trade. They also disliked war.

Some precepts of this liberalism, such as representative government, go back even further. As early as the 15th century, well before Edmund Burke hit the scene, men like Sir John Fortescue and John Seldon were extolling the virtues of English constitutionalism.

The liberal world order they and others helped build was one in which self-government and all it stands for — property rights, due process of law, universal suffrage — reign supreme over the desires of autocrats and their imperial and kleptocratic tendencies.

In the hands of the United States, the liberal world order changed in a fundamental way because the United States often intervenes in international conflicts for altruistic reasons. No other hegemonic power — say, Spain in the 16th century, France in the 19th century or England in the 19th and 20th centuries — has ever intervened in so many foreign conflicts with no immediate benefit to its home territory.

Take Korea, for instance. Had the United States not intervened in 1950, the Communist takeover might have been much swifter and more severe. In the 1990s, the United States got involved in wars in the Balkans and Kosovo ostensibly to stop ethnic cleansing. Other examples, like Vietnam and Iraq, are more controversial and ambiguous but nevertheless demonstrate America’s desire to bring about positive change in faraway countries without the motivating factors of imperialism or territorial expansion that underlay the foreign intervention of previous hegemonic powers in world history.

There is an invisible, yet vital, global benefit to America’s continued overseas presence: the survival of a liberal world order.

That liberal world order is now in danger. American scholar Robert Kagan recently gave a talk at Stanford University about America’s unique role in maintaining the current liberal world order. He called it “The Jungle Grows Back.” America’s continuing dominance, economically and militarily, he argued, is quite literally the only thing keeping “the jungle” — that is, non-liberal powers — from reclaiming the world.

Kagan argues that, notwithstanding the British origins of Western liberalism centuries before the discovery of the Americas, liberalism has only been effective since the United States intervened in World War II and defeated Germany and Japan.

Because of America’s response in World War II, the illiberal countries of Germany and Japan reformed and adopted Western liberal democracy. They now embody the type of predictable (some say boring) way of life afforded under Western liberal democracy. They are also at peace with their neighbors. Of course, the direct benefit of this, for America and the rest of the world, is the greater opportunity to improve society and the pursuit of happiness that comes with great powers at peace. Thus, rather than engaging in wars to line its own coffers, as imperial powers do, the United States often spends more money than it comfortably can in support of this international stability.

Kagan’s view is not without its critics. Paul Pillar, a realist writer, recently claimed in his book, “Why America Misunderstands the World,” the United States may believe it is acting in everyone’s best interest, but it doesn’t actually understand the rest of the world because it is isolated by a “moat” of two oceans. So when it acts on the world stage, it is in fact overstepping its boundaries and stepping on everybody else’s toes — even if it thinks it is doing the right thing.

The Trump administration claims to adhere to the realist school of foreign policy. The NSS begins, “An America First National Security Strategy . . . is a strategy of principled realism.” In defining that principled realism, the NSS continues: “We are also realistic and understand that the American way of life cannot be imposed upon others, nor is it the inevitable culmination of progress.”  This is a direct dig at Bush’s engagement in nation-building  to bring about more Western liberal democracies in the world.

Yet if the NSS does in fact shape the Trump administration’s approach to the world, what are the consequences of this approach? What does the future look like if America shirks its global leadership role? Does China take over the role of nation-builder, as it appears poised to do in Syria? Does Russia hold all the cards in the Middle East after backing Bashar al-Assad (and winning)? If these are the consequences, the forces of illiberalism are once again winning, and the world is going backward into the future.

Woody Allen famously quipped that “80 percent of life is showing up.” The same is true in diplomacy. If America does not show an interest in solving the world’s problems, other nations will gladly show up and reap the rewards.

It is understandable that Trump’s vision of a restrained America appeals to the American people, weary after 16 years of war. This view, while potentially popular, is shortsighted. Trump, a sometime populist, appears to be setting security policy according to how he can mollify his constituency and solidify his own leadership. His efforts at self-preservation, however, come at the expense of America’s strategic interests, including its role as preserver of the liberal order.

What Trump and war-weary Americans miss is that withdrawal from the global stage doesn’t just mean coming home. It means creating a vacuum — one which countries like China, with its booming economy and growing military strength, are eager to fill.

Western culture will not be dominant forever. Americans need to look up from current domestic distractions and realize they still have a vital role to play in the world. For now, to borrow a line from Kagan, they are “world order maintainers.” That may not be the most popular explanation of America’s role in the world, but it may well be the most important one.