This is an interesting article which tell us that what is happening in US will affect the global stock market.
Read: U.S. Crisis Underscores Global Links

Why? Here is one of the reason:
“People thought that was just a U.S. phenomena but it does affect the rest of the world because, as we discovered, the lenders to all those leveraged deals were just as much financed by foreign banks as U.S. banks,” Ugeux said.
The stock market is highly related with other market and it is important for you to have your eyes and ears open to the other stock market around the globe too.