A more complex reason is the rise of the information age and the global market. Put another way, it is now more profitable to conquer consumers instead of territory. This approach creates wealth that allows government leaders to beat their swords into lower tax rates and reduced trade barriers. Then there is the decline of the dictators, brought on by the incessant pressures of information flow, and the attraction of freer markets and societies. History suggests that kaisers, Fuhrers, emperors and tyrants of all stripes have been more likely to start a war than democratic leaders.
Political freedom favors peace, as do freer markets.
Thomas Friedman of The New York Times once observed that no two nations with McDonald's franchises have ever gone to war. But don't try to sell that kind of stuff to civilians of the former draft age. They know what they want and do not want. A survey of potential volunteers by the Army shows 11 percent said they probably would join or consider joining one of the military services, against 54 percent who definitely would not. Young people apparently no longer equate military service with patriotism.