If you have the time, I highly recommend Mark Blyth's explanation of the EU situation. The article is mostly right. Blyth goes into a lot more detail in the history (pre-euro), showing how the various banks of europe bet against their own sovereigns by exploiting how the bond yields were converging with the introduction of the Euro - often by getting all the Greek and other "risky", high-yield debt that they could.

If you thought "too big to fail" was bad enough in the US, at least our Fed could do something other than let the economy fail and now were starting to slowly recover. In Europe, they are "too big to bail", and I expect a few more countries to quickly follow Greece's lead fairly soon.