Risk sharing  Economists like Peter Kenen 5 pointed out more than 40 years ago that a functioning monetary union was predicated on risk sharing between its constituent entities.
The calls which I discussed just now for a lender of last resort to be introduced for sovereigns can be seen as just as much of a manifestation of these thoughts as the notion of introducing in the euro area a common unemployment insurance scheme, or, taken to the extreme, mutual liability in the form of euro bonds.