Identify a very important date in European history. Without this event, or had it happened differently, how might history have come out differently?
Perhaps the most important date in recent European history was January 30, 1933. This was the date that Hitler was sworn in as chancellor of Germany.
If Hitler had not been named chancellor of Germany, things might have come out so very differently. Without Hitler, one could argue, there would have been no WWII. Without WWII, there would have been no Holocaust. There would have also likely have been no Cold War. In fact, it is not even clear that the US would ever have become the major power in the world. Without the Holocaust (and to some extent the Cold War) Israel would probably never have come to exist as a country. If all of these things had happened/not happened, the world would be so different today that it is essentially impossible to imagine what it would be like.
I agree that 1933 may have been a watershed year, but for another reason. In that year that Professor John Atanasoff at Iowa State University thought of using capacitors to store data.
This message, one of billions stored in computers, is stored in a computer that uses capacitors to store information one bit at a time one bit per capacitor.
This idea ranks with the invention of written language, the invention of paper, and the invention of the printing press in the way it changed history.