Thanks to President Trump’s “America First” rhetoric and the rise of populist-nationalist parties in Europe, there’s a lot of debate about “nationalism” these days. On that subject, as on so many others, it’s worth listening to Pope St. John Paul II, not least because last month marked the 40th anniversary of his epochal Nine Days in Poland in June 1979 — days on which the history of the 20th century pivoted in a more humane direction.