I should point out something else --
If any country in the world is bankrupt, it's too bad for that country and its people. Greece, for example. Their options are limited.
But the United States of America is a unique case among ALL the countries on the planet. Even if the USA is bankrupt, they can simply print more money. The USA is literally the king of the world, since it controls the World Currency, also known as the US Dollar. What other currency is tied to OIL which everyone needs? Yes, if any country wants oil, they have to hold and use US Dollars to purchase that oil. That bolsters the US Dollar, and puts the United States in a very favorable position.
If any other country printed millions of extra units of their currency, their unfortunate country would suffer instant hyperinflation. But the Dollar has much more "mass" because there is much more to back it up. So the effects aren't felt as much, or as quickly. The USA can get away with MUCH more printing press activity.
So it figures that even though many countries' stock markets are collapsing -- and continuing to collapse even today -- that the stock market of the USA will end up in the POSITIVE today, even after being down 1000 points, because "we're awesome like that" and have an all-powerful printing press that can work market voodoo.