The Civilization on the Edge of Forever.
By a strange set of events (which are inconsequential to my line of though here) Spock and Kirk are forced to time travel. They end up in late 1930s New York City and wind up living among the destitute. They quickly come to the attention of a woman by the name of Edith Keeler who runs the mission they work at and hang out at.
Spock jerry rigs up a device to read his recorder and play it back. One of the results of this playing back of the recording (Spock was recording the events that led up to their needing to time travel) showed the woman Kirk was falling for was a saint needed to die. Why? In the original set of historical events she died and early death and was of no consequence, we know the world events from the 1930s and 1940s. In the track of history they were on, the 1930's and most particularly the 1940s were way out of whack.
Edith Keeler rose to national prominence as a pacifist leader and delayed the entry of the United States into WWII. This as it turns out gave the Third Reich time to develop nuclear weapons before anyone else and the rest is alternative history as they might say. As it turns out Kirk and Spock correct the historical accident by letting a road traffic accident (RTA) occur unhindered that McCoy prevents in the alternative history.
Think of what might have happened if Hitler would have developed nuclear weapons prior to the Allies? A ferry load of Norwegian civilians were killed because their ferry carried German heavy water, and Werner Von Heisenberg was targeted for assassination.
Is this the log we are rolling on now? I fear the pacifists could be leading us to another fools bargain right now. 10 lives saved, $100.00 for now for 1,000,000 lives and $1,000,000,000 in the future.
I am sure I am not the only one to have blogged on this episode of Star Trek with this context.