Have you ever seen Star Trek episode "The City on Edge of Forever"? If you haven't:
Commander McCoy accidentally makes himself delirious, beams down to a nearby planet, goes through a portal back in time to 1930s, and changes history by saving a woman. This causes Starship Enterprise to cease existing.
So Captain Kirk and others who followed McCoy to planet are stranded and have to go through portal to save McCoy, stop him from changing history, and bring back Starship Enterprise and their buddies left on board.
They arrive a few days before McCoy and while there Kirk falls in love with a social worker, Edith Keeler. But Spock discovers that in order to repair history she will have to be killed in an auto accident.
Furthermore, if she lives, she will lead a pacifist movement that makes President of U.S. delay entering WWII. This will allow Nazis time to be first to make atomic bomb and take control of world.
So Kirk has to make a decision: let McCoy save Edith and change course of history forever or stop McCoy and save world from dictatorship.
Do you ever wonder if history would have turned out same way if even one thing had been changed? If one person had lived or died? If one event had or had not taken place?
History is really mysterious in that way, because you never know if one minor incident in whole thousands of years of history could have had huge effects we never even thought of.
I've realized that Internet is same way. It has allowed us to do business and live life like we never have before.