First, I don't think it's likely that we'll see the dissolution of the United States of America. I suppose it's barely possible that an issue that sufficiently polarized "blue states" and "red states" might end in a separation. However, as that's already failed once in American history, I doubt it would work better now. 
I think it's entirely likely that a hundred years from now, and possibly much longer, the center of North America will still be politically identified as the USA. However, I think it's also entirely likely that, in practice, it will bear little to no resemblance to the governmental system we recognize and were taught about in grade school (which, of course, in practice bears little resemblance to the intentions of the Founding Fathers).
The thing is, there's no single issue, crisis, or turning point that can be identified as The Real Problem or the Wrong Decision or The Beginning of the End. As always, it’s the "slippery slope" effect - one little thing seems reasonable. Then one more little thing isn't that much of a change. Then five years later, you're so used to those things that another little change is tolerable. Over time, dozens of small changes add up to big differences.
Let's consider just one small subset of the problems I see in the US: potential effects of the various anti-terrorist measures. Individually, they can sound reasonable. In the climate of fear and suspicion immediately following the terrorist attacks , there were very few people arguing against what was intended to be an immediate change for everyone’s safety. But what did we get out of that?
A) The Office of Homeland Security. Why can't the Department of Defense defend us? Well, they handle the external threats and Homeland Security is intended to handle the internal threats. Okay, fine. It doesn't even sound that bad to say that we're using ordinarily forbidden procedures to get evidence against suspected terrorists, to identify them faster and prevent them from acting. As long as nothing is done without evidence, maybe not so bad. But who decides who's on the list? If one unethical person adds one person they dislike to the list, it's being used highly improperly. If one unethical person highly placed gets to use an entire department to pursue their own goals, by masking them in the approved goals, we get HUAC and McCarthyism. It has not happened yet, to the best of my knowledge. But the slippery slope means that it could, if we get complacent and do not pay attention.
B) The Patriot Act. I don't know half of the ramifications of this particular mess. However, I do deal with one bit of it on a regular basis. All parties to real estate transactions must have their names compared to a list to make sure they aren't suspected terrorists. In practical terms, this means one more $10 charge by the title insurance company for the additional search. However, it's a lot of hassle to clear up when a name turns up that is same name, different person. All those other people who share your name, who you learn about when you search your own name on Google? Better hope that none of them have done anything shady. I've heard stories about the no-fly list that are along the same lines, although I don't know if that also stems from the Patriot Act or not. Honestly, I think one of the best signs for the US is that people, and especially politicians, are beginning to object to all of this and reconsider it.
C) A War on Terror that's been much more aggressive than the War on Drugs. Again, not arguing the immediate retaliatory strike against the directly responsible parties. I personally disagree, but my personal beliefs are not viable on a national level. However, at the time, the political climate was such that expressing disagreement with the actions of the President was very unwise indeed. Now, civics classes taught me that it is not just my right, but in fact my responsibility, to question the actions of elected officials and tell them when I disagree. There's something very, very wrong when that becomes socially unacceptable. Again, that's largely improved. However, the war proceeded to a less obviously involved target. Then there are rumors that there may be further targets. Then there's what it's doing to the already somewhat shaky international relations with the countries we aren't trying to fight.
And all of that is just one small part of the problems I see. Others include: the international perception of the US versus the US perception of the US; the two-party system, when one of the parties fails but there's nothing to replace it (again, possibly getting better - but it's hard to say); a "mandate" being defined as "winning an election without the help of the Supreme Court"; and attempts to impose a moral code on others, which dovetails nicely into the rant palingyuan requested. So, To Be Continued...
 You know... splitting the country doesn't sound like such a bad idea, overall, when your side is the strong minority. All of a sudden I understand the Confederacy much better.
 In passing, it occurs to me that a civil war now would probably end in a decisive victory for the South. Interesting...
 Incidentally, that's when the terrorists succeeded, not when they crashed planes and destroyed buildings and lives. Saboteurs are trying to cause damage. Terrorists are trying to cause terror. When we panic, they win. I am NOT criticizing individual fear reactions - that's largely uncontrollable anyway. And I still get shivers down my spine every time I see a low-flying plane. But I don't let it stop me from getting on a plane to travel, or from expecting a certain amount of privacy and liberty in my personal life.