The confluence of matching points we have between the market of 1929 and our current market have gotten to be scarily similar over the last 5 - 10 years.
For us to match the DJI of 1929 we'd need;
A slow uptrend with regular pullbacks/crashes. A couple 50% crashes spaced a bit apart from each other. A breakout of the high of these crashes into a sheer up-trend. This uptrend to run a bit over 300% before it started to show warning signals.
This is an unlikely series of events that has not happened before. What we're seeing in the US indices now is a signal seen once in this lifetime (For most of us).