"The analogy that is at the heart of this book is about a jungle and a garden," says Robert Kagan. "In order to have a garden and sustain a garden, you've got to be constantly gardening. For me at least, that is a good analogy for this liberal world order, which itself is an unnatural creation which natural forces are always working to undermine." Human nature has not fundamentally changed, and this peaceful period is an aberration.