Italy is the fourth-largest economy in Europe and the eighth-largest economy in the world, and its banking system is collapsing. And Germany is desperate. It must maintain its standard of living. It can only do that with exports and Deutsche Bank is very exposed to Italian debt. But so is the rest of Europe.

Because the US has control of the sea. Because the US has built up its wealth. Because the US is the only country in the world really not to have a war fought on its territory since the time of the Civil War ... Therefore we can afford mistakes that would kill other countries. And therefore we can take risks that they can't ... the core answer to why the United States is like this is we didn't fight World War I and World War II and the Cold War here.

Recent presidents have gone off on ad hoc adventures. They have set unattainable goal because they have framed the issue incorrectly, as they believed their own rhetoric.

War is an extraordinary condition to be in - to be, for example, in the combat information center of a warship [and behaving] as though you were merely processing credit card applications. [Instead,] the information you're processing is that an incoming missile is 15 kilometers away, now 10 kilometers away, now 5 kilometers. You have to separate yourself psychologically from the fact that your mortal existence may well end. That is the ancient reality of war.

Constraint theory argues a number of things. First, that the impossible has to be identified. Second, that the actor is then constrained by circumstances to act a certain way. For example, should we invade ISIS? Can we invade ISIS? What would it take to invade ISIS? Once you ask that question you discover the price of that option and then you take a look at American politics and see that the country is probably not prepared to invest the 2 to 3 million people that it would take to defeat ISIS and the insurgency afterwards. All right, so that's not going to happen.

But every time new powers emerge they have to find their balance. New powers are emerging, old powers are declining. It's not that process that's dangerous, it's the emerging position that's dangerous.

Now if you can recognize and memorize a grandmaster's game, and you have the respect to understand [Zimbabwean president Robert] Mugabe who has survived past anyone's expectations, and make the simple assumption it wasn't an accident, and you understand why he did what he did, now you're ready to predict ... The key to forecasting is to understand both the constraints nations are under and the manner in which the struggle for power shapes leaders.