Fences may make bad neighbors, but rivers can drive them wild. When the flooding Rio Grande between El Paso and Ciudad Juárez switched course in 1864, it hefted the U.S.-Mexican border south and thereby shifted to the U.S. an arid, chop-shaped patch of land known as El Chamizal (The Thicket). The transfer exacerbated American-Mexican relations for a century.
Last week, in a cordial exchange of abrazos and acreage, Presidents Lyndon Johnson and Gustavo Díaz Ordaz redressed the Rio Grande's trespass. Crossing into bunting-festooned Ciudad Juárez, they spoke at the monument erected by Mexico to commemorate the settlement. "An old argument has...