Donald Trump raised eyebrows recently when he demanded that the U.S. complete a wall with Mexico–and that Mexico pay for it. But give the Donald this: he tapped into a global trend. Several border-wall projects are under way worldwide, from India, which has a long-standing project to fence off much of Bangladesh, to the E.U., where anti-migrant sentiment runs high after incidents in Calais and the Mediterranean.
Saudi Arabia will soon have a 600-mile (965 km) wall on its border with Iraq, adding to the 1,100 miles (1,770 km) of barrier that already exists between the Saudis and Yemen. Turkey is spending hundreds of millions of dollars to erect a wall along its southern border with Syria in order to fend off would-be terrorists–only to find itself on the receiving end, as E.U. member Bulgaria puts up its own wall with Turkey. Hungarian Prime Minister Viktor Orban wants to complete a fence being built to curb illegal immigration from Serbia.
Walls are the archetypal quick fix. They reassure the public that there will be a sharp separation between “them” and “us.” In Israel, the construction of a fence in the West Bank has coincided with a dramatic reduction in suicide attacks, encouraging other countries to add concrete and barbed wire.
Yet Israel’s experience may be more exception than rule. Walls don’t deter migrants, who simply take longer, harsher routes. Walls are incredibly costly to build and maintain. They can disrupt trade and hurt a country’s reputation. Nor will walls solve terrorism. Tunisia is building a wall to separate itself from chaotic Libya, but it will not stop the more than 3,000 Tunisians who have reportedly traveled to fight in Syria from coming home.
Rather than building walls, politicians need to address root causes. In Europe, that means financing local development across the Mediterranean to reduce migrants’ incentive to leave their home countries. Those kinds of sober, long-term strategies won’t make Trump happy. But then, what will?
This appears in the August 17, 2015 issue of TIME.