Alternate timeline episodes

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A list of episodes where we see an alternate timeline. For a list of episodes where we see a parallel universe see Parallel universe episodes. For a list of episodes that feature actual travel through time see Time travel episodes.

[edit] Star Trek: The Original Series

Episode	Time Periods	Cause	Effects
"The City on the Edge of Forever"	1930-2267	Edith Keeler's death averted by McCoy	Nazi Germany lasts beyond 1945, United Federation of Planets does not exist

[edit] Star Trek: The Animated Series

Episode	Time Periods	Cause	Effects
"Yesteryear"	2269, 2239	Death of Spock as a child	Amanda Grayson has died, Thelin became USS Enterprise's first officer

[edit] Star Trek: The Next Generation

Episode	Time Periods	Cause	Effects
"Yesterday's Enterprise"	2366	USS Enterprise-C went through a temporal rift in 2344	Federation embroiled in long war with Klingons

[edit] Star Trek: Deep Space Nine

Episode	Time Periods	Cause	Effects
"Past Tense, Part I"	2024, 2371	Gabriel Bell dies	Federation does not exist, Romulans encroach on Alpha Centauri
"Past Tense, Part II"	2024, 2371	Gabriel Bell dies	Federation does not exist, Romulans encroach on Alpha Centauri

[edit] Star Trek: Voyager

Episode	Time Periods	Cause	Effects
"Non Sequitur"	2372	Timestream	Harry Kim did not join USS Voyager, Daniel Byrd joined instead
"Year of Hell"	2374	Krenim weapon ship	Numerous incursions
"Year of Hell, Part II"	2374	Krenim weapon ship	Numerous incursions

[edit] Star Trek: Enterprise

Episode	Time Periods	Cause	Effects
"Twilight"	2153-2165	Interspatial parasites	Archer removed as Captain of Enterprise, Xindi destruction of Earth and human colonies