War to me is very much like sex. You can develop a theory that says sex is primarily for the exchange of genetic material, or that it's a celebration of life, or you can make up 50,000 theories about why human beings have sex, all of which are in some sense true, all of which by themselves miss the point. Because the answer is extraordinarily complex. It may be for fun, it may be for reproduction, for financial reasons, any number of things.

While certain coastal cities have become very prosperous, the rest of China has a per capita income of $200 a year. The coast wants to have nothing to do with the interior; it wants to work with Tokyo and New York. This is an old story in China. It is why Mao succeeded in 1927. He wanted [coastal] Shanghai to throw the foreigners out, but Shanghai was doing too well financially [to expel foreigners]. So Mao went to the interior and raised a peasant army. He came back to Shanghai and sealed off the country.

When you're young and going to war, it's a genuinely exciting moment. You are going to risk yourself. On the battlefield, you are suddenly free. You realize: I'm here, I'm in it. Exaltation. Suddenly you're hit by another extraordinary feeling: my God, I can be killed. And: will I embarrass myself? It's like you're in a kaleidoscope and all of these extraordinary feelings are zipping by.

By the 20th century, war ceased to be an encounter between two armies. It became an encounter between two societies, because a factory worker producing a gun or a bomb is as deadly as a pilot.

When you have the countries like Germany, China, and Russia decline, and be replaced by others, that's when systemic wars start. That's when it gets dangerous, because they haven't yet reached a balance. So Germany united in 1871 and all hell broke loose. Japan rose in the early 20th century, and then you had chaos. So we're looking at a systemic shift. Be ready for war.

When I went to war, I did not go making geopolitical calculations. I went to war with a lust.

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.