I was recently given the unique privilege of viewing a remote, yet extremely important tract of land that cuts the Korean Peninsula in half. It is known as the DMZ—the Demilitarized Zone—or by the infamous reference “The 38th Parallel.” In all, it is 250 kilometers long and 4 kilometers wide. To call it “demilitarized” is a bit of dark humor. Made of earthen walls, concrete, and barbed wire, this border is interrupted only by guard towers manned by soldiers with automatic rifles.

With the use of a pair of field glasses, I could see the guard posts of the North Korean People’s Army (KPA) across the wide expanse of this No Man’s Land, and if you looked very carefully, you could even make out the dark figures of the sentries themselves. It’s a dangerous place. Those occupying the 150 guard posts on the northern side of the wire have been known to shoot more than a few people on the southern side.

Since the Korean War ended in July 1953, more than a thousand South Koreans, Americans, and other citizens of countries that comprise the forces of the United Nations have been killed along this stretch of hotly contested land. As recently as 2015, North Korea lobbed a few shells into a nearby South Korean village to destroy, of all things, loudspeakers playing K-Pop. I’ve heard of asking your neighbors to turn down their music, but this is taking it to a whole new level.

MULVANEY SAYS BORDER WALL WILL GET BUILT, 'WITH OR WITHOUT' FUNDING FROM CONGRESS

As the soldier guiding me pointed out various aspects of this barrier, I couldn’t help but think of the current controversy surrounding Trump’s proposed border wall. More than that, I thought of border walls throughout history and their purposes.

Here are a few:

The Great Wall of China. Purpose: To keep people out. Effectiveness: Not very. Stretching more than 13,000 miles, this is the Mother of All Walls. I even rappelled off of it once. While it was a formidable deterrent to raiding parties, it did nothing to keep the Mongol out.

The Walls of Athens. Purpose: To keep people out. Effectiveness: Highly effective. During the Peloponnesian War (431-404 BC) the Athenians withdrew inside the formidable walls of their city when the Spartans invaded. Supplied by the sea, they could wait out any siege. In the end, Athens lost the war, but it wasn’t due to the weakness of her walls.

Hadrian’s Wall. Purpose: To keep people out. It stretches 73 miles near the border of Scotland and England. Effectiveness: It might have been very effective if the Roman hadn’t enacted their own version of a government shutdown and abandoned Britain altogether.

The Walls of Jerusalem. Purpose: To keep people out. Effectiveness: Twice the citizens of Jerusalem defiantly took refuge within their walls confident they were safe and twice they were destroyed. All that remains is the Wailing Wall.

The Berlin Wall. Purpose: To keep people in. Effectiveness: So long as the GDR lasted, this wall did what it was supposed to do. But then President Ronald Reagan traveled to Berlin and made one of the most iconic speeches ever: “Mr. Gorbachev, open this gate! Mr. Gorbachev, tear down this wall!” Two years later, Berliners did it themselves.

As you can see, border walls have a checkered history of success and, well, a checkered history. But those who built them to keep people out generally had good reason for doing so. Every nation has the right to protect its way of life from those who threaten to destroy it no matter if that threat takes the form of overt force of arms or that of a human tide whose sheer numbers will overwhelm the existing social, political, and cultural order.

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This brings us back to the wall where I was standing just a few hours ago. The DMZ is the kind of wall Democrats would have you believe President Trump wants to build: a threatening, barbed-wired symbol of tyranny. Nonsense. For the North Koreans, the wall is meant to keep people in; for the South Koreans, it is meant to keep them out. South Koreans aren’t fighting to cross the wire in a desperate bid to reach the communist Utopia of North Korea any more than Americans are crossing the Rio Grande into Mexico to take advantage of that country’s wonderful social welfare benefits and overturn their electoral process through illegal voting.

The great irony of all of this is that while Democrats would do little to defend the frontiers of the United States, Americans have been shipped around the world to defend this one for decades. Common sense says that we should defend our own borders before we even consider defending those of other nations.