Why are we so rich? An American earns, on average, $130 a day, which puts the U.S. in the highest rank of the league table. China sits at $20 a day (in real, purchasing-power adjusted income) and India at $10, even after their emergence in recent decades from a crippling socialism of $1 a day. After a few more generations of economic betterment, tested in trade, they will be rich, too.

Actually, the “we” of comparative enrichment includes most countries nowadays, with sad exceptions. Two centuries ago, the average world income...