Way back when, (you'd have research the period) Greece was either on the verge of, or in bankruptcy. As Greece is part of the EU, many EU banks would have to absorb the losses It caused, and still causes, quite a stir in the news.at the time, since the EU felt the Greek government, (IIRC), and it's president had caused the massive debt, through their lavish spending habits.This is a myth. While yes we owe China a lot of debt its not the majority of it(6%). Add on the fact the whole world is in debt, China is on the downswing in growth, and Europe also has piling problems its not just the US.
Here's the Wiki page on Greece's current issues, as well as those of its past: https://en.wikipedia.org/wiki/Greek_government-debt_crisis
The moral of the story is, the US dollar is fairly stable in spite of out debt situation, while some other country's financial systems are one the verge of collapse.