This is what part of the U.S. and Mexico border looked like in 1898, just an open strip of land with train tracks going across. Here’s what that same stretch looked like 110 years later, in 2008. The open land is split by a fence. A border gate replaces the train tracks. So how did we get here — from open desert to a patchwork of highly politicized border barriers? To understand, we’re going to focus mostly on a single location, in Nogales, the spot where this stone monument marks the border line. What happens here tells the story of the border’s transformation, the how and the why. We’ll begin in 1848. The United States has just defeated Mexico in a war over expansion. Mexico is forced to sign away more than half its land and sell a bit more later on. This is how the U.S. got the land which includes today’s border, but there’s no fences or barriers yet. No. First the border just gets marked, in many places with nothing more than a pile of stones. These stones are at the spot I mentioned that we’re going to focus on, outside a saloon in Nogales. The saloon is on the U.S. side. There’s essentially free movement back and forth. But these rocks hardly mark the border accurately. The border stays like that for 43 years until 1891. That’s when the U.S. and Mexico set out to define the border with better accuracy. Stone monuments go up at regular intervals to clearly mark it. If we go back to the saloon, Monument 122 stands where the pile of rocks once was. The monument will remain, but the saloon will be torn down. Why? In 1897, the president orders that several buildings be demolished in order to clear a 60-foot-wide path along the border. Mexico has already done this. The path is cleared to make smuggling easier to spot. Not drug smuggling — this is smuggling of everyday goods to avoid import and export taxes. The new tract of open land also emphasizes the growing separation between Mexico and the U.S. Still, there’s no border fence in Nogales, not yet. But in rural areas, there’s a problem only a border fence can solve: ticks. In the early 1900s, ticks are causing disease among cows in rural areas. Those cows are crossing back and forth over the border. So the first-ever border fence is actually built to keep cows from spreading disease. But what about the first fence meant to control human movement? There are three big reasons the U.S. invests in more security at the southern border, culminating in the first permanent fence. Number 1, racist attitudes towards Chinese people had led to law banning their immigration to the U.S. The law was enforced mainly at water ports, but less so on the Mexican border. So going through Mexico became an easier way Chinese people could avoid the ban and still enter the U.S. But the large number of people showing up along the southern border eventually drew stricter security. Then in 1910, a revolution breaks out in Mexico. That leads to reason Number 2 for a security buildup. The U.S. sends troops to the border to stop the fighting from spilling over. Here’s that monument I showed you earlier, where the saloon once was, this time in 1913. Then — World War I — reason Number 3 for the security buildup. U.S. troops stay on the border. There’s paranoia in America that German spies might cross over from the Mexican side. All this violence and intrigue creates a tense atmosphere on the border. Small gunbattles erupt between jittery American and Mexican forces. Each side blames the other. So here’s where the first permanent border fence to manage human crossings comes to be, in 1918. It’s made of wire — very basic. You could easily climb over the fence if you wanted to. But its purpose isn’t to wall off the two countries. The fence is a way to diffuse the tension and control the flow of growing border traffic. Then, Prohibition happens. Alcohol is legal in Mexico. So yeah, a lot of American visitors go there. The U.S. monitors crossings to enforce the regulation of American morality, as one researcher puts it. Also, population along the border is growing, so we see the border fence get enhancements in the late 1920s. It’s got barbed wire at the top. Lampposts are installed. New stone pillars form crossing gates. Prohibition gives way to the Depression and then World War II. Here’s where the U.S. starts to use barriers to really keep people out. A program is bringing Mexican workers into the U.S. to beef up the wartime labor force. “The term most commonly used is Braceros.” But at the same time, other Mexicans without authorization to enter the U.S. sneak across the border anyway, looking for jobs. This photo shows a U.S. border agent demonstrating how easy people can get through a rural border fence. So all of this leads to more fences and more border patrols. The racial slur in this newsreel title shows the prejudice towards Mexican workers during this time. The U.S. places more restrictions on Mexican immigration in the following decades. That begins a cycle that continues to this day. Less ways to legally enter the U.S. means more people crossing the border illegally, which leads to more deportations. To build stronger border barriers, the U.S. uses surplus from the Vietnam War. See right here: It’s a helicopter landing mat. Mats like these line the border in the 1990s. Meanwhile, the U.S. is increasing roundups of undocumented immigrants. “There is too much of it, and we must do much more to stop it.” Then we come to Sept. 11. That brings strong bipartisan support for more border security. “This bill will make our borders more secure.” And the length of the border wall expands to five times what it was, even though the number of illegal crossings are going down. “We have more of everything — ICE, Border Patrol, surveillance, you name it.” Border security remains a huge rallying cry. “We’ve got to have a wall. If we don’t have a wall, it’s never going to end.” “A wall is an immorality. It’s not who we are as a nation.” And so the debate continues. That’s how we got here. Barriers have existed along the border for a long time, but their purpose has been ever-changing. So five minutes into the video, you saw how Vietnam-era landing mats were used to help construct the border fence. But there’s another surprising material that was also used: During World War II, the U.S. forcibly confined people of Japanese ancestry to internment camps. Those camps had fences, and some of those fences were reused later on to build the Mexican border fence. This time not to keep people in, but to keep people out.