It is sometimes said that walls are ineffective when preventing the entry of large numbers of desperate economic migrants. This isn’t so. The energy mustered by the home population when protecting their territory is more than fully equal to the task. In many species of animals and birds, opportunistic males, however powerful or desperate, seldom manage to evict a resident male from his own territory.
The EU wall, or fence, starting in the northernmost tip of Finland — to keep out migrants coming through Russia — and zig-zagging southwards through the Balkans until it reaches the Mediterranean, is a good example. Over the course of a year it is probably successful within a dozen or two individuals. The only weak spot in the EU border is the sea-borne route between Libya and Sicily used by young Africans. What are now modest numbers of them are now accumulating in Italy — and still being refused jobs in a country which is on the verge of a declining population!
The Mexico-Texas wall was partially built in President Bush’s time, and there’s no reason why it shouldn’t be finished off relatively quickly. Perhaps it ought to be now in order to assuage half the American electorate but mainly to allow Trump to save face and greatly modify many other of his hastily signed Executive Orders, many if which are abhorrent to any modern advanced civilization.