Pax Americana?

Too early to say. But here's some suggestive evidence.

The number of genocides and politicides plummeted by 80% between 1988 and 2001.
The number of armed conflicts around the world has declined by more than 40% since the early 1990s.

International crises, often harbingers of war, declined by more than 70% between 1981 and 2001.

The number of refugees dropped by some 45% between 1992 and 2003, as more and more wars came toan end.

The period since the end of World War II is the longest interval of uninterrupted peace between the major powers in hundreds of years.

The number of actual and attempted military coups has been declining for more than 40 years. In 1963 there were 25 coups and attempted coups around the world, the highest number in the post–World War II period. In 2004 there were only 10 coup attempts--a 60% decline. All of them failed.

As they say, read the whole thing. Especially if you want to jump on the 2001 date as the end point for several statistics.