The United States does not need, nor does it want, its very own Iron Curtain. Without even considering the ecological disaster a wall would create, what Trump proposes would be a perpetual “black hole” for our public money, for staffing and maintenance. And it would, as walls inevitably do, make perpetual distrustful enemies of neighbors who should be perpetual friends and allies. The migration of people has been a continuous part of what it is to be human for tens, if not hundreds of thousands of years. As ever in the past, climate change and population growth have been underlying causes. In these times, walls and armed repulsion do nothing to address underlying needs. They just add to the misery of everyone concerned — and we all are concerned. We must join the rest of the world and address the actual underlying causes — climate change, overpopulation, uneven distribution of wealth and resources — and stop any tendency to behave as though throwing up walls, putting innocent people in corrals, and making enemies of neighboring nations is some sort of solution. It is not. We need to use our vaunted human brains and work together to deal with trends that have been predictable for decades, but unaddressed in the way humans always have of postponing addressing or even acknowledging difficult problems until they become disasters.