Krugman's theory is that European economic integration got too far ahead of political integration, and therefore there's no political decision-making body to think about the good of the whole European entity rather than the individual good of each nation:
The economies of Europe’s many nations are almost as tightly linked as the economies of America’s many states — and most of Europe shares a common currency. But unlike America, Europe doesn’t have the kind of continentwide institutions needed to deal with a continentwide crisis.At the end of his piece, Krugman says that Spain may be a pivot-point, because Spain (like Florida in the US) was a haven for overcomsumption based on credit that was too easy:
This is a major reason for the lack of fiscal action: there’s no government in a position to take responsibility for the European economy as a whole. What Europe has, instead, are national governments, each of which is reluctant to run up large debts to finance a stimulus that will convey many if not most of its benefits to voters in other countries.
As in Florida, boom has now turned to bust. Now Spain needs to find new sources of income and employment to replace the lost jobs in construction. In the past, Spain would have sought improved competitiveness by devaluing its currency. But now it’s on the euro — and the only way forward seems to be a grinding process of wage cuts. This process would have been difficult in the best of times; it will be almost inconceivably painful if, as seems all too likely, the European economy as a whole is depressed and tending toward deflation for years to come.