Could you handle the wait? When last I wrote, we were languishing in the 19th century, an era of free trade halls and the march of reason. Now fast forward to the 20th century.
Liberalism took a bit of a battering with the outbreak of the Second World War... maybe international disputes were not so peaceably resolvable after all. Paradoxically, the Cold War was good for Liberalism... if the other side had some big ideology they could wave in our faces then didn't we need something too? Realism and its pure power politics is too depressing as a basis for organising, and anyway leads to the worrying conclusion that we are no better than they, so Liberalism, or a somewhat weird version thereof, became the ideology of the West.
Still, in academia, things are maybe a bit more subtle. There are a couple of things you can see as at the heart of Liberal thought. Market economics as a good thing remains central. Democracy is also usually seen as a good thing. Like the Realists, Liberals see the state as the primary actor in international politics, and like them they also see states as having interests which may conflict with each other. However, Liberals see this conflict as being potentially manageable. Crucially, the world is not set up in a zero-sum manner, and it is possible for states to cooperate in such a manner that everyone benefits. International institutions come into being as ways of promoting particular types of inter-state cooperation while regulating state conflict. In certain circumstances international organisations can gain a life of their own, and become themselves serious players on the world stage.
The early 1990s saw Liberalism reach its high tide mark, with all that end of history stuff about how Liberalism had won and how there would henceforth be no serious challenge to its conceptual hegemony. More recent events have suggested that to the extent that Liberalism is identical to the West (whatever that is), there are many people in the world who want nothing to do with it. It is maybe also interesting that the intellectual cheerleaders for Bush's war on terror and the invasion of Iraq are essentially purveyors of Liberalism, albeit of a muscular and combative sort. Although classic Liberals would see democracy as being a fundamentally good thing for people to have, they may well not have thought that bringing it to them at good point was particularly likely to be successful, but this is life.
One final fascinating Liberalism fact arises out of something Kant predicted. I mentioned how he thought that republican regimes would eschew war. This has not obviously come to pass - many of the world's great warmongers are blessed with representative government. However, one thing is very striking, and demonstrable by empirical research - in general, representative democracies do not fight wars against each other. This contrasts with other systems of government, where there is no obvious sign of intra-system war avoidance.