Niall Ferguson says it's no surprise Trump's so popular

"The United States of Amnesia," says Scotsman Niall Ferguson, "needs to take history more seriously."

Ferguson, you won't be surprised to learn, is a historian. He is a professor at Harvard University and a senior fellow at Stanford University's right-leaning Hoover Institution.

Ferguson, unlike pundits across the country, wasn't surprised by Donald Trump's rise from reality-TV star to Republican presidential nominee. In fact, he says any historian worth his salt should have seen him -- or at least his "movement" -- coming.

For the most part, Trump is selling straight-up populism. And five "ingredients" are necessary for populism to succeed, Ferguson said at a recent Google ZeitgeistMinds event.

"The first ingredient for a populist backlash," Ferguson insisted, "is an increase in immigration."

Check. The percentage of the U.S. population that is foreign-born stands at 13 percent right now, which is very close to the historic high during the Great Melting Pot days of the late 19th century. More important is how dramatic the recent increase has been. The foreign-born population in 1970 was only 4.7 percent.