If history teaches us one thing, it is this: Empires tend to crumble from the inside. If history teaches us two things, it is that very few people ever see it coming. Perhaps it is because of those two lessons that George Santayana’s famous line continually rings true, across civilizations and across the ages: “Those who cannot remember the past are condemned to repeat it.” Time and again, once-great countries have failed because their citizens thought it never could happen to them. They thought they were immune. They thought they were different. They thought they were better. They were wrong. That is the danger facing America today. The 2.4 million men and women in our armed forces can and will defeat any foreign enemy we face—but it’s no longer foreign threats that pose the greatest danger to our future. Indeed, as Tocqueville presciently warned, we are our own greatest danger. We are on the verge of “stamping out” ourselves. In other words: We have met the enemy … and he is us. The real battle we are fighting right now is with the laws of economics—and it’s a war that can’t be won. It’s like attempting to fight gravity by constantly jumping: There are slivers in time when it might feel like you’re winning, that you’ve actually changed the laws of nature. Then you crash back to earth and, eventually, get too tired to jump anymore.