The sight of thousands of poor people walking hundreds of miles to escape poverty and violence is tragic (see above picture from the Wall Street Journal), whatever one thinks of open immigration. The story reveals lots of problems. Let me focus on one that may have been unnoticed.

In a tweet of October 18, President Trump wrote:

In addition to stopping all payments to these countries, which seem to have almost no control over their population, I must, in the strongest of terms, ask Mexico to stop this onslaught – and if unable to do so I will call up the U.S. Military and CLOSE OUR SOUTHERN BORDER!

What does he mean by “these countries”? He probably does not take “country” in the sense of geographical features, like when we say “this country has high mountains.” He probably does not mean the population of these countries, because he would then be saying that these populations have no control over their populations. Granted that a political theorist could refer to a sort of social contract whereby the people of a country would have agreed to prevent themselves from fleeing. But it is unlikely that they would have unanimously agreed to a sort of Berlin Wall. At any rate, it is not sure that Mr. Trump completely masters complex contractarian models.

Perhaps he meant that all the South American governments should collectively control all their populations. But we wouldn’t expect such an interpretation from a nationalist who believes in national sovereignty.

What Mr. Trump presumably meant is that “the governments of each of these countries seems to have no control over its population.” This is a quite remarkable statement. Why would it be good that a government controls its population and can prevent its members from leaving? And if that’s good for other countries, is it good in the United States too? Shouldn’t it be the population that controls the government, not the other way around?

Like all issues, the problem of migrations can be approached in a collectivist-authoritarian or individualist-libertarian way. There are many arguments, methodological, economic, and ethical that favor the second approach. This implies a presumption of individual liberty.

On the specific problem under consideration, two easy—if admittedly incomplete—solutions should be obvious, assuming the U.S. government adopts the correct approach. First, “trade, not aid” or, in this case, “trade, not threat.” If poor South American workers had open access to the American market for their goods, they would have better hope of escaping poverty while staying put. Second, stopping the tragic war on drugs would probably much reduce gang violence in these countries. If American consumers want something, don’t prevent the foreign poor from selling it to them.