The President of the United States wants to buy an icy northern territory from a foreign country. Critics hate the idea and mock it as absurd and wasteful. But the President makes the deal, and the purchase proves to be one of the most brilliant geopolitical deals in history—a huge boon to American strength and prosperity. Am I describing the 45th President’s effort to buy Greenland from Denmark? Nope, I’m describing the 17th President’s successful effort to buy Alaska from Russia in 1867. It was one of the best bargains America ever struck. If President Trump can pull off another...