First, trade and globalization have reinforced the trend toward democracy, and democracies don't pick fights with each other. Freedom to trade nurtures democracy by expanding the middle class in globalizing countries and equipping people with tools of communication such as cell phones, satellite TV, and the Internet. With trade comes more travel, more contact with people in other countries, and more exposure to new ideas. Thanks in part to globalization, almost two thirds of the world's countries today are democracies -- a record high.

Second, as national economies become more integrated with each other, those nations have more to lose should war break out. War in a globalized world not only means human casualties and bigger government, but also ruptured trade and investment ties that impose lasting damage on the economy. In short, globalization has dramatically raised the economic cost of war.

Third, globalization allows nations to acquire wealth through production and trade rather than conquest of territory and resources. Increasingly, wealth is measured in terms of intellectual property, financial assets, and human capital. Those are assets that cannot be seized by armies. If people need resources outside their national borders, say oil or timber or farm products, they can acquire them peacefully by trading away what they can produce best at home.

Griswold notes that much of the political violence left in the world is concentrated in Africa and the Middle East; it’s no coincidence that these two regions are the least integrated into the global economy.