Which historical event would you change and why?

[sharrukin]

The overthrow of the Russian provisional government by the Communists.
The rise of Hitler would have been much more difficult as many of his followers who had been former socialists or communists would not have been as great a force in Germany. He would not have been able to use the communist threat of a takeover of the German government to advance his own agenda. Russia would have been spared the nightmare of communism and the cold war would not have been so ideological in character. I suspect there would have been some rivalry but it would not have taken on an almost religious tone.

[caesar44]

1914 put some poison in hitler's soup , but alas , this is just a dream

[Somebody Else]

I would prevent the first ever separation of a monocellular organism. Would make things so much easier.