At the end of World War I, everyone was certain of two things: that long trench-to-trench wars were bad and weapons of mass destruction needed to be banned. Acting together, the leaders of the Western world forbade chemical weapons and made a mutual agreement (the prototype of future U.N. agreements) to punish any nation that used poison gas. At the time, there were serious thinkers who also wanted to ban aerial bombing. If they had, England and the United States could not have waged war, fire-bombed whole cities and nuked nonmilitary targets as they did in World War II.
Two things are obvious to me when I reflect upon how the history of the 20th century informs our current conflict in Syria. Wanting to avoid extended involvement and "boots on the ground" is noble but impossible, and focusing on an adversary's use of a banned weapon, such as nerve gas, only leads other world powers to commit larger, more indiscriminate, acts of mass killing.
Future wars will not be about political process, i.e., colonialism versus anarchy or democracy versus communism. They will be about access to and participation in the global society. We need to be involved in the Middle East because it and sub-Saharan Africa are the critical places where people are ready to participate in the global village, but their leaders won't let them. Future flashpoints will be around things such as gender equality, free trade and Internet access. The postmodern world is going to be both bloody and complex. We need to stop thinking like we did at the beginning of the last century.