Part 1 here.
When I wrote part one, it didn't occur to me that it was the day before 9/11. Spent most of that day reading all sorts of stuff, all over the sphere. Overall, I think this scenario is less likely than I did 10 days ago, but that doesn't matter- I'm trying to imagine a scenario in which a Civil War within my lifetime is possible.
2011: Nukes hit the Eastern Seaboard. Besides the massive loss of life, economic loss, etc, this has some political effects. The US becomes somewhat more polarized politically. A large number of the bigger companies in California leave for parts of the midwest, both avoiding ever increasing state taxes and for security's sake, in case there's a strike off the Western Coast. This leads to an increasing spiral, tax base leaves -> the underclass refuses to let payouts decrease, so taxes increase in the upper brackets -> tax base leaves. Hollywood still exists as a brand, but nearly all movies are made elsewhere. As upper and middle class leave, housing prices drops dramatically, leading to the loss of significant amounts of cash on paper, especially for the middle class. The loss of things as they were leads to massive protests, which are as incomprehensible to the soccer moms and military dads in Texas and Colorado as the French students protesting for lifetime employment starting at 18 or illegal aliens wanting anglos out of California.
The blast in Washington didn't kill the President, the Vice President, or a significant fraction of Congress, but it killed 6 of 9 Supreme Court Justices. The highest levels of the federal government move to a secure military base; the surviving bits of the lower levels stay around what was Washington DC or decentralize. Large portions of the federal government exist only on paper.
From this point there would need to be some scary trends: (1) the US splitting into those who want a diplomatic, fortress USA solution, and those who want to go to full war footing against a large fraction of the Islamic world; (2) the Supreme Court going for some ... interesting, international flavored interpretations of the Constitution, especially the first and second amendments; (3) with some successes against the Great Satan, fascist Islam strengthens drastically, leading to the US having no favorable ties to any Middle Eastern regime, and the invasion of what is left of Israel.
After that, perhaps, northwestern US tries to leave, possibly joining Canada. This might even be acceptable, given the drastically lowered federal power, except for one thing: the Alaskan oil fields, which had not been tapped due to environmental protests, and which are vital given the reduction in Middle Eastern oil.
Beyond that, I don't know. Some technical changes in the next twenty years? Drastically increased longevity? Bioenhancements as common as breast augmentation is now? Improved computing power to the point of true AI? A true epidemic, whether natural or man-made? Significant space colonization would make a big difference, but I can't see than happening in the next 50 years without alien contact.