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.

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.

Italy spills over to everything. Italy is a huge banking system. It has been the major banking system in Eastern Europe. It's worked with Austria's banking system. There's all sorts of interplays there. So it's not the PIIGS one should worry about. Germany hasn't even begun falling yet. And when Germany falls, and it will, that's when the panic begins to set in.

There is a radical and unprecedented shift [in war] that is part of the general transformation of civilization. First, understand that the past 150 years of warfare are totally unprecedented in that we introduced a breathtakingly inefficient technology: guns. In the First World War, and this is not an exaggeration, it took 10,000 rounds of ammunition to kill one person. Any given shot had a one in 10,000 probability of ending someone's life.

The importance of the question and the availability of an answer are two different things. I'm not willing to state that because the question is fundamental, therefore I possess the answer. And I'm certainly not willing to say that since I don't possess the answer, I'll pretend that I do.

The important thing in war is that there is an element of rage, but you must remain very distant from it.

The tragedy of the human condition is that the thing that makes us most human - community - originates in the inhumanity of war.