It could cascade into a world wide bankruptcy and then depression. It'll start with the Euro countries throwing in the towel, one by one. The people in these countries say FU to their Governments and vote populist/socialist leaders into power. But that won't matter (look at California), Banks around the world will start to fail, like dominos. The world's currency system will be obliterated. Governments will have to wipe the slate clean and their citizens will lose everything except their physical posessions... Therein lies the pretext for martial law!
Mike