How do you distinguish a foreign policy “idealist” from a “realist,” an optimist from a pessimist? Ask one question: Do you believe in the arrow of history? Or to put it another way, do you think history is cyclical or directional? Are we condemned to do the same damn thing over and over, generation after generation — or is there hope for some enduring progress in the world order? 

For realists, generally conservative, history is an endless cycle of clashing power politics. The same patterns repeat. Only the names and places change. The best we can do in our own time is to defend ourselves, managing instability and avoiding catastrophe. But expect nothing permanent, no essential alteration in the course of human affairs.

The idealists believe otherwise. They believe that the international system can eventually evolve out of its Hobbesian state of nature into something more humane and hopeful. What is usually overlooked is that this hopefulness for achieving a higher plane of global comity comes in two flavors — one liberal, one conservative.

The liberal variety (as practiced, for example, by the Bill Clinton administration) believes that the creation of a dense web of treaties, agreements, transnational institutions and international organizations (such as the U.N., NGOs, the World Trade Organization) can give substance to a cohesive community of nations that would, in time, ensure order and stability.

The conservative view (often called neoconservative and dominant in the George W. Bush years) is that the better way to ensure order and stability is not through international institutions, which are flimsy and generally powerless, but through the spread of democracy. Because, in the end, democracies are inherently more inclined to live in peace. ...