Should We Just Open the Borders?

If you wanted to pinpoint an exact date when the United States became destined to be a global superpower—a nation rich beyond its wildest dreams, able to enforce its will around the world—you could do worse than February 2, 1848. With a few quick pen-strokes on the Treaty of Guadalupe Hidalgo, the Mexican-American War ended, and the landmass of the United States grew by 25 percent. Importantly, that 25 percent included the territory that had, up to that point, been known as Alta California.

The central valley of California...