Conditions for perpetual peace

In a review of Steven Pinker’s The Better Angels of Our Nature, Bill Gates said that the book "stands out as one of the most important books I’ve read – not just this year, but ever". Who am I to disagree? The book is an unbelievably rich resource documenting the steady decline of violence throughout history. To get an impression of how strong this decline has been, take a look at this graph.

I came across countless things I did not know. I did not know how pervasive this decline of violence was, let alone that I had any idea about why this was so. The famous German philosopher Immanuel Kant (1724-1804) formulated his ideas about this in his 1795 anti-war document "Perpetual Peace".

First he suggests six preliminary steps toward perpetual peace, being: "that peace treaties should not leave open the option of war; that states should not absorb other states; that standing armies should be abolished; that governments should not borrow to finance wars; that states should not interfere in the internal governance of another state; and that in war, states should avoid tactics that would undermine confidence in future peace, such as assassinations, poisonings, and incitements to treason."

Then Kant suggested three conditions for perpetual peace:

1. that states should be democratic (or "republican') and have a government dedicated to freedom, equality and the rule of law;
2. that "the law of nations shall be founded on a Federation  of Free States" which would provide objective, third-party adjudication of disputes. 
3. that there be universal hospitability or "world citizenship", meaning that people from one country should be free to live in safety in others, as long as they don't bring an army with them. "The hope is that communication, trade, and other "peaceable relations" across boundaries will knot the world's people into a single community, so that a violation of rights in one place is felt throughout the world. 

Sometimes philosophy is approached with some dedain by people claiming that it is just a waste of time. But propositions by philosophers can sometimes be tested systematically and that is what two political scientists, Bruce Russett and John Oneal, did with Kant's three conditions for perpetutal peace. They analyzed a huge database containing data about interstate wars using multiple regression. They found that 1) democracies are less likely to get into military disputes, that 2) countries that depended more on trade and the global economy, were less likely to have a military dispute, and that commerce has robust pacifying effects, and 3) that membership in intergovernmental organizations favors peace. They conclude that Kant got it right.