Steven Pinker

As I argue in a recent book which is (in part) complementary to John's (The Better Angels of Our Nature: Why Violence Has Declined), I think that the causes of war -- human avarice, short-sightedness, vengeance, dominance, tribalism, and self-deception -- will always be with us, but that wars may not be (at least, not in the sense of big interstate wars that kill a lot of people -- local skirmishes and small civil wars that blend into turf battles and mafia-like feuds will be with us a lot longer). The more institutionalized the practice (as in human sacrifice or chattel slavery), the easier it is to abolish, and big interstate wars are highly institutionalized, hence the decline we've seen since 1946 could very well continue until the practice no longer exists.