Some charts from historical tops in the Dow, starting with 1901:

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The giant gap down above did not happen in a day. The government forced the closure of the NYSE on July 27 (after a crash when the closure was foreseen), and it was not reopened until Dec 14. The Great War started in the interim.

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In May 1940, where you can see a crash above, the Low Countries fell to Germany and Northern France was occupied. However, charts alone were all you needed to be bearish.

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