I certainly won't be the first person to offer comparisons to the Great Depression of the 1930s with what's occurring now. But for sake of argument the patterns and even the seasonal dates are quite similar.
Election cycles are similar while the structure of the Dow Jones Industrial Average is quite different with just a few companies then even existing today. Nevertheless history can repeat and we don't have another market to compare current data to.
The monthly chart from the 1930s extends far beyond what we can offer now and we're not even attempting to be clairvoyant. One observation and conclusion is during the 1930s there were great rallies followed again by major declines. This made the rise in 1933-36 for example just an impressive bear market rally.
That said chart patterns are stunningly similar made more so by today's news the eurozone has entered another recession not seen since 2009. With the world highly interconnected economically and many global market indexes well-correlated one to another makes these chart views more than just a little interesting.
Draw your own conclusion from these views and we'll have to wait and see if the future follows the past.