AMERICA is a country built by immigration, but nothing in its history compares to the rise in its Hispanic population. Changes to immigration law in the 1960s triggered a decades-long surge in arrivals, taking the Hispanic population from just 7m in 1970 to 57m today, a number that is set to double by mid-century. At that point one in four Americans will be of Latino descent. In relation to the population of the day, there have been proportionally larger surges in the past, notably involving European migrations in the 19th and early 20th centuries. Two factors make the rise of...