Psychology, to a certain extent-- the subprime thing still has people spooked, and Monday the US markets weren't open. Most people walk through life assuming the worst and without the US markets as a bulwark of... well, I won't say sanity, but at least optimism, the rest of the world went into freefall. More, on any given day, the US markets open last, or close to last, so the rest of the world had like a day and half to two days of total fucking irrational panic.

As of right now, the S&P is only down about 0.6%, although it opened down more than 3%.

My guess is that everyone around the world sold everything they thought they should sell, woke up this morning with pissbuckets of liquid assets, realized that the US markets were not melting down as badly as anywhere else, and put their spare cash right here.

Go, us.