Two weeks ago, I pointed out that we live in something close to the best of times, with record worldwide economic growth and at a low point in armed conflict in the world. Yet Americans are in a sour mood, a mood that may be explained by the lack of a sense of history. The military struggle in Iraq (nearly 2,500 military deaths) is spoken of in as dire terms as Vietnam (58,219), Korea (54,246) or World War II (405,399). We bemoan the cruel injustice of $3 a gallon for gas in a country where three-quarters of people classified as...