Why do some states default on their debt more often than others? We argue that sovereign default is the outcome of a political struggle among different groups of citizens. It is more likely to happen if: (i) domestic debt-holders are politically weak; (ii) the political costs of the financial turmoil typically triggered by a sovereign bankruptcy are small. We show that these conditions are in turn more likely to be present if a country lacks a politically strong middle class and/or a sufficiently independent central bank.