First and foremost, walls in history have usually been built primarily for military purposes - to stop military invasions. One very famous wall that sometimes gets mentioned is the Great Wall of China. This is what China Travellers website has to say about the purpose of that wall:
The Great Wall of China was built to protect China from its enemies and invaders from the North, especially the Mongols. The Mongols were a tribal group that would regularly conduct raids into China. Despite the wall, the Mongols eventually conquered China. The Wall also kept Chinese citizens from leaving China.I would draw your attention to the fact that "Despite the wall, the Mongols eventually conquered China." It was big, and beautify, and ultimately didn't work.
Another example of a wall built for military purposes is the Maginot Line between France and Germany. Built after WWI, this wall was supposed to deter another German invasion of France. And while the wall itself was well made and strong, it obviously didn't stop the Germans from invading in WWII. In fact, it was so unsuccessful in producing its ultimate goal that it has become synonymous with a false sense of security. In fact, Merriam-Webster defines Maginot Line as follows:
These walls were built primarily for defensive, military purposes and they ultimately failed. So let's look at a wall that was built primarily for immigration purposes - the Berlin Wall. The Berlin Wall was built in 1961 to stop people from leaving East Berlin for West Berlin. According to Wikipedia:1 : a line of defensive fortifications built before World War II to protect the eastern border of France but easily outflanked by German invaders2 : a defensive barrier or strategy that inspires a false sense of security
Before the Wall's erection, 3.5 million East Germans circumvented Eastern Bloc emigration restrictions and defected from the GDR, many by crossing over the border from East Berlin into West Berlin; from there they could then travel to West Germany and to other Western European countries. Between 1961 and 1989 the Wall prevented almost all such emigration.Ah ha! A successful wall you say. Yes, it was a successful wall, but it was also a very well guarded wall. Again from wikipedia:
The barrier included guard towers placed along large concrete walls, accompanied by a wide area (later known as the "death strip") that contained anti-vehicle trenches, "fakir beds" and other defenses.It was also only approximately 87 miles long. Trump is asking for a much longer wall to be built - anywhere from 234 miles to 1000 miles according to a report from cnbc.com. And even the very effective Berlin Wall was not perfect. Going back to the Wikipedia article:
During this period over 100,000 people attempted to escape and over 5,000 people succeeded in escaping over the Wall, with an estimated death toll ranging from 136 to more than 200 in and around Berlin.And let us not forget who wanted that wall torn down. I believe it was the much revered (in some circles) Ronald Reagan who famously said "Tear Down This Wall." In the late 1980s, a wall built for retarding illegal immigration was seen as a threat to freedom and liberty. So why is one such a good idea now?
These are some examples of why I assume walls don't work and are a bad idea. Where there is a will, there's a way. People will always find a way around, over, through, or under a wall. Building a wall doesn't get to the root of the problem, it just spends a lot of time, money and effort to reroute the problem.
Let us remember also that walls in the past have not just been built to keep people out, but also to keep people in. I'm reminded of "Mending Wall" by Robert Frost, in which he says:
And, as Reinette (aka Madame De Pompadour) reminds us in "The Girl in the Fireplace" episode of Doctor Who:Before I built a wall I'd ask to knowWhat I was walling in or walling out,And to whom I was like to give offence.Something there is that doesn't love a wall,That wants it down.
A door once opened may be stepped through in either direction.A wall, once built, blocks passage from both directions. Think about it.