If your economy is shit, how are you going to pay the money back? Cutting funding to eduction? Letting your utility systems fall into disrepair? Not paying people to work?
I work in debt collection, and honestly there are some people who just are NOT going to pay the money back. They either lack the capital(no home, no car, no real money in the bank) or they lack the ability(old, injured, disabled, etc...). Greece has no capital save it's sovereign territory, and with a shit economy they also lack the ability to pay back their debts. Honestly, demanding poor nations pay back ever-growing debts is a waste of time. In the future: don't loan them money. For now: move on to better prospects.
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No. Greece isn't going to pay the money. It doesn't have it. How can it pay it? Even if it paid it, it'd only be paying like 1% annually, taking it hundreds of years to pay off the debt. Not paying it off isn't significantly different than paying pennies on it. Also, the actual value of American investment in Greece is fairly small. Greece does not owe almost 1/2 of all American money invested in Europe.