[Nick1984]

In terms of global stability the growth in the BRIC nations (Brazil, Russia, India, China) which has been pushing double digits if not close to it for a long time now should act as a counter to any US troubles. To me it seems simply since a lot of Western nations have been suffering from the effects of debt driven growth unchecked, the world is not shifting its resources to these new areas.

Like Dogpile just said, should a high beta sector have a sudden boom due to a technological advancement or some other factor then that could stall any downtrend in the US markets. With horrible lending practices to the public sector in the residential mortgage market many consumers should be feeling the squeeze on the hip pocket as mortgage repayments become to burdensome. This in turn will effect spending power to pump more money into the consumer goods and services sectors which in turn hurts those company's bottom lines.

Until the market shakes out all the bad debt in the US I think that in the medium turn the US will have more volatility but I won't speculate on the direction of that volatility. Money will continue to shift to those other markets and a housing price downturn in the short to medium turn in many Western countries (you can see that about to start happening here in Australia already) will have increased volatily even should markets turn around and start heading back up. The swings will be more frequent and more wild.