According to The New York Times in late 2011, “How European sovereign debt became the new subprime is a story with many culprits, including governments that borrowed beyond their means, regulators who permitted banks to treat the bonds as risk-free and investors who for too long did not make much of a distinction between the bonds of troubled economies like Greece and Italy and those issued by the rock-solid Germany.” In going through these culprits and how they interrelated, it should not be lost that the market mechanism itself can be held as suspect, for at the very least it enabled the furtive games to be played for far too long. Indeed, the market itself did not do a good job for years in providing accurate risk-return relationships.
The full essay is in, "Essays on the E.U. Political Economy," available at Amazon.