Obviously this has been honored more in the breach than in reality, but the idea that Nations with national identities were the unit of political organization - rather than principalities with feudal identities - is an idea that comes down to this very day.
In a strange coincidence, today also saw the founding of the United Nations in 1945, perhaps the high water mark of the Westphalian system.
The system is running down. As governmental bureaucracies have gotten stronger, there has been a series of catastrophes to western populations. The trenches of World War I, the death camps and bomber fleets of World War II, the Gulag, the financial collapses of 1986 through 2008* - and the impending collapse of the Euro Zone have drained the Westphalian System of the sense of legitimacy that has stood since 1648. Indeed, today's Progressives push a trans-national, post Westphalian vision which is essentially today's system dialed up to 11.
Never mind that devolution of power has been the name of the game for a quarter century. The dissolution of the Warsaw Pact, the breakup of Yugoslavia, the establishment of the Scottish Parliament as a serious political entity, the increasing willingness of state Governors to tell the Washington to drop dead: this is where the action has been.
Add to this the inability of our current elites to deal with non-Nation State actors like al Qaeda, or with Non-Governmental Organizations (NGOs), and the system is clearly out of gas. What comes next is anyone's guess. The only thing that's clear is that it won't be more centralized, with more control from an unaccountable elite. Just watch them as the wheels come off the Euro, perhaps starting this week. These are not the folks who will lead us to the Post-Westphalian system.
* By another strange coincidence, the financial collapse of 2008 also occurred on October 24.
UPDATE 24 October 2011 10:27: Must read at Isegoria's on the inability of the Westphalian system to deal with piracy anymore:
When not even states’ elites believe in the state anymore, why should anyone else? Piracy not suppressed represents history lifting its leg on the whole state system.Nothing says that the Westphalian system can't be replaced with international chaos.