Like self-proclaimed “rational optimist” Matt Ridley, the historian Paul Johnson contends there’s little evidence supporting the gloom-and-doom prophecies that have cropped up periodically since the end of World War II.

In a Forbes column, Johnson rebuts pessimistic arguments about climate change, overpopulation, and war.

This year marks the 67th anniversary of the end of World War II. The world hasn’t exactly been a peaceful place since the war. A recent Hoover Institution study shows that, in addition to civil wars and violence from piracy and terrorism, the number of minor conflicts between two given power groups has actually increased, yet the degree of violence in our global society appears to be in a long-term decline. Why? The single biggest reason is the absence of a general war ­between great states. A 67-year period without such a war is unprecedented, certainly since the disintegration of the Roman Empire in the 5th century A.D.

What’s behind this long interval of general peace? Almost certainly the ­existence of nuclear weapons and the unwillingness of the great powers to risk their entire structures and populations in a thermonuclear exchange. But the de facto ban on such weapons is unlikely to survive a proliferation of them among the small (and more belligerent) powers.

This is why we must prevent Iran from acquiring the bomb–quite apart from its brutal threat to use it against Israel. Even if it takes physical intervention by the U.S. to keep Iran in check, it will be well worth it, because such a demonstration of American willpower will deter other rogue states from going down the path Iran has chosen.