United States. Teetering on the edge of financial crisis and massive debt failure. When the feds fail, you'll have to all fight for yourselves.
Early in our history massive debt was used to keep the independent states in line as a (mostly) unified country. If the European Union were to accept responsibility for all of its members' debt in exchange for substancial political powers over them that would basically be what the US did over 200 years ago. I doubt debt alone is going to kill us. And even if bankruptcy kills a good chunk of the federal government as we know it today, you're not going to see any state try to go it alone either (save maybe Alaska, its never unwise to underestimate the chance Mrs. Palin doing something rash).
Would it lead to substantial social strife? Yes, but that's going to be throughout state lines, not between them. The vast majority of Americans cannot even tell you if their state is a net recipient or provider of government money, making some of the arguments the Scots are hearing right now independence useless. And centuries of free movement between states, and the out stretched familial, social and economic ties that it produced will not be undone short of anything but military force or equivalent disaster.
In short, I doubt think we're going to see the Disunited States of America in our life time, no matter how bad our politicians get.