“The era of the Monroe Doctrine is over,” proclaimed U.S. Secretary of State John Kerry on November 18. That was a historic proclamation, but what he said next was perhaps more surprising: “That’s worth applauding,” he said. “That’s not a bad thing.”

And with that, America proudly rejected a 200-year-old pillar of its foreign policy.

The arrogance is astounding. According to Kerry, the nearly 40 presidents who upheld the Monroe Doctrine did so for no good reason. It was a foolish, evil, imperialist doctrine, he appears to think. Finally, we have a president and secretary of state wiser and more virtuous than all those who went before.

The Monroe Doctrine states that any attempt by European powers to expand their control in the American hemisphere would be treated as an act of war by the United States. The spirit of the doctrine, brought up to date by former Defense Secretary Caspar Weinberger, is “that there should be no interference, no sponsorship of any kind of military activity in this hemisphere by countries in other hemispheres.”

America’s rejection of this doctrine is part of a foolish foreign policy that is imperiling American interests around the world.

Has the Monroe Doctrine proved worthless? Far from it.

One president who, perhaps more than any other, upheld this doctrine was Theodore Roosevelt. Roosevelt oversaw America’s transformation from a regional power to a world power. It was a dangerous point in American history, where jealous rivals looked for ways to forestall the ascendant America.

Roosevelt’s policy of aggressively confronting any threat long before it became serious meant that none of these threats materialized. But only because of his constant vigilance.

For years, America was ignorant of the fact that it had come within hours of war with Germany over the Monroe Doctrine in the winter of 1902.

That December, Germany, Britain and Italy began to blockade Venezuela in an effort to force the nation to pay back the debts it owed them. Roosevelt sympathized with their motives and did not oppose the blockade. He was, however, deeply suspicious of Germany. Britain, he knew, respected the Monroe Doctrine, and during the 19th century probably did more than America to uphold it. But Germany resented it. German naval chief Adm. Alfred von Tirpitz, for example, wanted naval bases in the Caribbean and Brazil.

In their communications with Britain, Germany noted that it was considering “the temporary occupation on our part of different Venezuelan harbor places.” Roosevelt was concerned they would repeat what they did in Kiaochow, China—where a “temporary” occupation turned into a 99-year lease.

So Roosevelt conducted America’s first large-scale naval exercises. Under the command of America’s most distinguished—and anti-German—military leader, Adm. George Dewey, these exercises had been long planned and had nothing to do with the Venezuelan blockade. Except for the fact that Dewey was ready to sail to war at an hour’s notice.

Germany backed down. Although the German Navy almost certainly could have beat America’s Atlantic fleet, it was dispersed and unprepared for war. Germany didn’t invade Venezuela, and instead allowed America to mediate in the disagreement.

Was Roosevelt right to be so bellicose? In 2002, historians discovered that as the Venezuelan crisis was unfolding, German strategists were drawing up plans to take Puerto Rico and launch a surprise attack on the American Atlantic coast. Roosevelt’s naval build-up soon made the plan unfeasible.

The world didn’t need to wait 100 years for more proof of secret German plans to attack America using Latin American and the Caribbean. After hacking German embassy diplomatic cables, British intelligence officers discovered that Germany was trying to persuade Mexico to attack America in 1917. The infamous Zimmerman Note, as it became known, helped bring America into World War i.

This is the real world. It is full of plots and intrigue. Nations are jealous of rich and powerful rivals, and look for weaknesses to bring them down. A toehold in Latin America could give the rivals the sort of advantage they are looking for.

This is why Tirpitz wanted a Latin American base. It’s why Iran and Hezbollah are forming ties with Mexican drug gangs, and why Russia pursued an alliance with Venezuela under Hugo Chávez.

But that’s not how America’s left sees the world. We’re all good people at heart, its leaders reason. If we sit down and get to know each other, there will be no war. We don’t need to look at history. They had wars in the past but that’s over now—we’re so much more enlightened.

Roosevelt built the Panama Canal so that America could quickly move its ships between the Pacific and Atlantic oceans, giving the American Navy freedom to concentrate its fire wherever it was needed. Today, America has given away that canal. Even its major military bases in Panama have been shut down. We don’t need to worry about things as old fashioned as power and enemies anymore, the thinking goes.

The Bible warns us that we are living in a fantasy. Deuteronomy 28 lists the punishments that will come upon Israel if it refuses to obey Him. Verse 52 warns that foreign nations “shall besiege thee in all thy gates, until thy high and fenced walls come down, wherein thou trustedst, throughout all thy land: and he shall besiege thee in all thy gates throughout all thy land, which the Lord thy God hath given thee.”

America will have its vital sea lanes cut off by foreign powers. That simply couldn’t happen without Latin America: It will require closing the Panama Canal to American traffic and having naval and aerial superiority in the Caribbean.

Just as Roosevelt oversaw America’s arrival on the world stage, President Obama is overseeing its retreat. The rest of the world sees a still-rich America becoming weaker and weaker. The temptation to undermine the nation has never been stronger. If America were concerned about its future, it wouldn’t reject the Monroe Doctrine, but rather increase its vigilance all the more.

Though America has grown unconcerned about it, the rest of the world is still playing close attention to Latin America. To take just one recent example, earlier this month Colombia sent a letter of protest to Russia after Russian bombers twice entered its airspace.

America’s geography—protected from the world’s major powers by hundreds of miles of ocean—is a blessing from God. In rejecting the Monroe Doctrine, America is negating, even rejecting, that blessing. Yet Mr. Kerry is proud of the accomplishment.

This wishful thinking—that sees the world full of happy friends—goes far beyond America’s rulers. It is the attitude of America as a whole. How much press coverage have you seen about the end of the Monroe Doctrine? It has not appeared in America’s newspapers. It isn’t just the leaders who are unconcerned—the media don’t even consider it news because their readers probably wouldn’t care if they read about it.

The nation is living in a make-believe world. The Monroe Doctrine was designed to protect the United States from foreign powers. It has been rejected because it no longer believes there is anything to be protected from.

But there are real dangers in this world. For more on what the world is really like, see our latest print edition of the Trumpet on the subject of life in the post-American world.