One of the most important developments in the modern world is the rise of democracies to becoming the dominant part of the world’s population, and economic and military power. The chief reason this unprecedented development is important is that only liberal democracies never fight wars with one another. The recent peaceful settlement of the crisis on the borders of Ecuador, Columbia, and Venezuela is a powerful illustration of this fact.
The pioneering work of Rudy Rummel powerfully demonstrates  that the democratic peace is significant statistically, and both he and I (scroll to here  and down to democratic peace article) have explained the reasons for this continued peace: that democracies are emergent orders and not hierarchical organizations, as are undemocratic states. Different dynamics apply to their behavior as systems, dynamics that tend to keep the peace when both parties are democratic.
For the first time in human history a solution to war might have evolved, and done so unintentionally. It does not guarantee peace. There are too many sociopaths in power and serving the role of neoconservative advisors to ever be 100% certain. But it is very unlikely.
The largest threat to that solution – the threat of the US Presidency evolving into a Caesarist dictator elected every four years – now seems destined to failure. A powerful executive independent of domestic democratic pressures is no more likely to keep the peace than any other kind of dictator or king, as Kaiser Wilhelm demonstrated so tragically in WWI. He is too insulated from what it is that promotes peace which are the dynamics of a democratic system far more than the character of the individuals who hold power.
This is the one area where Prof. Rummel and I parted ways. He supported our imperial venture against Iraq because he believed the Bush administration intended to build a democracy there and that once Hussein was gone it would be possible to construct one. I opposed it because I believe democracies have to build on internally generated institutions currently lacking in Iraq and because the centralizing of American political power would weaken the reasons for the democratic peace by moving us towards a government like Wilhelmine Germany: a dictator abroad with democracy locally.
I believe events have demonstrated who was correct here. There are things we and other democracies can do to promote more democracies, but imposing them violently on cultures with no previous experience of basic free institutions is not one of them.