10 Star Trek Timelines That Were Erased

The City On The Edge Of Forever is one of the earliest examples of Star Trek episodes that pack a whallop. The reason that it works as well as it does, thanks in no small part to the acting on show, is the fact that there is no other option: Edith Keeler must die.

Many characters in history are remembered for what they did. Edith is remembered as the voice of peace who was killed outside of her Mission. Had she survived, she would have set the human race on a far darker path than she ever intended. In the 23rd century, the Enterprise discovers Carl, then in the form of the Guardian of Forever. A drug-crazed McCoy jumps through this time portal, then all goes dark. 

The landing party, protected in the eddies of time emanating from the device, find that they cannot raise the ship on hails. As far as they know, there is no ship, no fleet, no Federation. Something very wrong has happened. McCoy, in his haste to do the right thing, saved Keeler in the past. She then continued her push for peace, delaying the United States' entry into WW2. The Axis powers won the war, leading to a timeline too dark to imagine.

Kirk and Spock travel to the past and stop McCoy, ensuring that Keeler has her meeting with that car. Though Starfleet and the future are saved, it is a sombre ending.