Hello, everyone. I’m urging you to do me the following favor. Get a copy of Robert Kagan’s recent book, “The Jungle Grows Back: America and Our Imperiled World,” and read it over the next few weeks. It’s a short book. It’s a brilliant book. It’s an exceedingly important book. And it explains a lot of things that may seem puzzling to you, as they do to me.

Kagan’s thesis is pretty straightforward. The world is much darker and more Hobbesian than we like to think. The liberal order that was created at the end of World War II — NATO, the Marshall Plan, America’s acceptance of its role as global policeman, or at least the nation that kept the sea lanes open for commerce — that set of ideas, institutions and international guarantees is not the natural state of things or the logical endpoint of the history of Europe. It was the creation of the United States in conjunction with our World War II allies, Britain and France, imposed on the two great defeated powers Germany and Japan, and maintained for the last seven decades by America’s understanding that however expensive and frustrating this enlightened settlement has been, it has been worth it because the alternative is chaos — madness, war, rapine, genocide, destruction — and this time chaos is armed with nuclear weapons.

Kagan says America has become weary of its role as the supervisor and fiscal agent for the liberal order. It’s expensive. Our allies don’t seem to pull  their own weight and they often criticize us for the hard work we do to protect their interests and territorial integrity. On the surface, it seems ludicrous for us to have troops stationed in Europe when the Cold War has been over for half a century. We have pressing domestic challenges to attend to here at home. As Donald Trump says, our airports suck. We Americans don’t really believe the world can spin out of control again, as it did in 1914 and then in 1939.

Kagan says that the last two presidents, Barack Obama and now Donald Trump, are products of that weariness. Sen. Obama voted against the Iraq War. That’s why he defeated Hillary Clinton in the Democratic primaries in 2008. As president he chose not to intervene in Syria, even though we probably needed to intervene in Syria. He responded to Russia’s absorption of the Crimea with some moderate economic sanctions — doesn’t sound like John Kennedy’s “pay any price, bear any burden, meet any hardship, support any friend, oppose any foe” declaration in January 1961. In Egypt, according to President Obama’s almost entirely unfair critics, he seemed even to be apologizing for America’s geopolitical mistakes.

And now Donald Trump. He pulled us out of the Paris climate accords, canceled the Trans-Pacific Partnership, repudiated NAFTA and went out of his way to insult our best friend in the world, Canada. He has denounced NATO as obsolete and, at NATO headquarters, refused to reaffirm Article Five, which declares that an attack on one NATO member must be treated as an attack on all of them, and that all NATO nations must defend whoever is being mistreated by the Russians. President Trump would like to close our borders and by executive order and some extra-constitutional actions has done what he could to wall out people he regards as undesirable.

Kagan’s book is not yet another attack on Donald Trump, but he makes clear that he believes Trump’s agenda is spectacularly, self-destructively and ruinously wrongheaded for the United States. He is plenty hard on Barack Obama too, but Trump is the nihilist who seems bent on dismantling or destroying the very liberal order that Kagan says has saved the world from madness and annihilation for the past 75 years.

Russia has absorbed the Crimea — the first territorial grab since World War II — and it is clear that Vladimir Putin would like to absorb Ukraine — the breadbasket of the former Soviet Union — and if he can find a way to get away with it, the Baltic states: Latvia, Lithuania and Estonia. When will Putin stop? Kagan’s view is that Putin will only stop when we stand up to him in a big way, which means war if necessary.

The title of Kagan’s book is chilling. He sees civilization as a kind of island of order, commerce and community carved out of the jungle. We thought after the Soviet Union collapsed and the Berlin Wall came down that the jungle was receding and would never encroach on the arts of civilization again. With the rise of nationalist movements in European countries, with Brexit, with Russia’s clear territorial ambitions, with the election of Donald Trump in the United States, with the backlash against refugees from broken Third World countries (most of them broken by us), Kagan sees the jungle creeping back into what we thought was a sacred enclave.

So please read this book right away and please let me know what you think.

Here’s the point I wish to make to the 40 million Trump supporters, who are cheering from the sidelines as he dismantles the liberal world order. Three things:

• First, it has been a bargain. We are not so much “giving it away” and letting our so-called allies take advantage of us. We are in fact making a sober investment in the only world where we can truly flourish. The failure of our bouts of isolationism before the two world wars of the 20th century proves that we cannot withdraw into fortress America.
• Second, (are you listening?), the prime beneficiary of the liberal world order is the United States of America. We get back much more than we give. Our investment in a stable world of territorial respect, tolerance, somewhat open borders and relatively free trade benefits America far more than it does other nations.
• And third, if you think that the world will lurch along just fine once we pull away, you haven’t done much reading or thinking. You certainly are not a citizen of Lithuania or Poland, South Korea, or the Ukraine.

The book is called “The Jungle Grows Back: America and Our Imperiled World,” It’s the most important book I have read in many years. I so very strongly urge you to start reading it today.