Across the world, building walls has become the political strategy favored by nations convinced that barriers are the only way to deal with difficult neighbors. In some regions, walls are used to claim territory; in others, they are used to separate warring factions; in yet others, they are meant to keep the unwanted out.
Donald Trump shares this view. The centerpiece of his presidential platform from the beginning has been building a wall between Mexico and the United States to stop illegal immigration, getting Mexico to pay for the concrete structure, and outlawing amnesty for immigrants already in the U.S. without documentation. (He presents this as a new initiative, without mentioning that the U.S. has just completed building 651 miles of fencing and walls along our southern border.)