The war between Hamas and Israel forces everyone to recognize an uncomfortable truth: Immigration is a foreign-policy issue. In Germany, as throngs of Hamas supporters took to the streets, Henry Kissinger told Welt TV, “It was a grave mistake to let in so many people of totally different culture and religion and concepts because it creates a pressure group inside each country that does that.” Americans have been shocked to see anti-Israel demonstrations in Britain, too — and to find college campuses in our country are deeply polarized by the bloodshed in the Middle East. At the Cold War’s end,...