 Long-term history in particular shows you the contrary to what the song says, the song of course says, what is it good for? Absolutely nothing. Contrary to what the song says, war does seem to have been good for something across the long run. Not good for everything obviously, but good for certain things. I think the evidence points us toward this kind of uncomfortable and paradoxical conclusion. And this is what I argue in this book, that across the last 10,000 years war has made larger societies that have made their subjects safer and richer. Question I raise in the title of the book in some ways is the most important question in the world. I mean we live in an age where weapons are more destructive than ever before and yet the world is in many ways safer than ever before. The first of the four claims that I make in this book is that by fighting wars people have created larger, more organized societies that have reduced the risk that their members die violently. Probably in stone age societies your risk of dying violently was somewhere in the 10 to 20% range which is an astronomical level of violence. Now if we fast forward to the 20th century, we fight two world wars, genocides are committed, nuclear weapons are used, somewhere between 100 million and 200 million people die violently in the 20th century, an astonishing number. But something like 10 billion people live during the 20th century and that's a 1 to 2% rate of violent death. The second claim that I make is that there's actually more to it than that. In addition to making us safer, these bigger societies have made us more prosperous as well. The peace creates the preconditions under which you can have more complex divisions of labor and more elaborate trade routes can develop and wealth can be driven up. Conquest tends to drive a spike in violence and destruction but if you come back to a place that's been conquered and absorbed into a larger society you come back a century or two later. Regularly what you find is that the place is more peaceful and more prosperous. The third claim which I think is very important for the argument as a whole is that war seems to be the worst possible way to do this, to make these bigger, safer, richer societies. And yet it seems to be pretty much the only way people have found. People hardly ever seem to be willing to give up their freedom which is of course what you do when you're incorporated into one of these bigger groups. Give up freedoms including the freedom to kill and impoverish one another. Hardly ever seem to be willing to do this without somebody forcing them to do so. Those are the first three claims. If they're true, I think that there is only one conclusion we can reach which is that war has been good for something. And in fact I suggest in the book it's been so good for something, for making the longer and making peace and prosperity that it's now beginning to put itself out of business. That we have weapons so destructive, organizations so effective that another great war could potentially destroy humanity altogether.