For you George Lindsay fans I might remark that the latest drop in the Dow looks like a continuation of the "five reversals" portion the domed house in Lindsay's 3 peaks and a domes house which I last commented upon here. So this week's low is probably point 20 and the Dow is likely to make higher highs at points 21 and 23 before the bull market ends.
I think world stock markets are being driven higher by active QE policies by the European Central Bank and the Bank of Japan. Moreover, the Bank Of China has gradually been adopting an easier monetary policy the effects of which are manifest in the big advance in the Chinese stock market this year. Until these policies are halted I think world markets will be moving generally higher. Of course there will be the occasional scary drop of 10-20% but I doubt we will see anything like a prolonged bear market lasting a year or more and dropping prices 25-30% until monetary polices change dramatically.