For the entire time I've been a fan I thought the Federation and the Klingons being at war in the 23rd Century was normal. Which is why I never got people being up in arms about a Klingon War in
Discovery. I don't want to get too much into it here because it's water under the bridge.
What I do want to mention is that I'm watching "The Emissary" (TNG). It's towards the beginning of the episode and K'Ehleyr talks about a Klingon Ship that had been in deep freeze for 75 years. Since "The Emissary" takes place in 2365, 75 years ago would be 2290. Between TFF and TUC. K'Ehleyr and Riker both mention the war between the Federation and the Klingons at that time.
Cutting and pasting the dialogue from the
transcript below...
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K'Ehleyr: Two days ago, Starbase Three Three Six received an automated transmission from a Klingon ship, the T'Ong. That ship was sent out over seventy-five years ago.
Riker: When the Federation and the Klingon Empire were still at war.
K'Ehleyr: The message was directed to the Klingon High Command. It said only that the ship was returning home and was about to reach its awakening point.
Picard: Which suggests that the crew had been in cryogenic sleep for that long journey.
K'Ehleyr: Exactly.
Riker: And when this crew is revived?
K'Ehleyr: We'll have a ship full of Klingons who think the war is still going on.
Picard: So our task is to find the ship, and tell the Klingons they're no longer at war.
Riker: Why us? Wouldn't a Klingon ship be a better choice?
K'Ehleyr: A Klingon ship, the P'rang, is on its way, but it's two days behind us. That may be too late.
Troi: Why too late?
Riker: When the T'Ong crew awakens it will be within striking range of several Federation outposts.
Data: There are thirteen colonies with minimal defences in that sector.
K'Ehleyr: Nice, ripe targets for a Klingon warship.
Troi: And you believe you can convince these Klingons that the humans are now their allies?
K'Ehleyr: No, not a chance. If you ask me, talking will be a waste of time. Klingons of that era were raised to despise humans. We'll try diplomacy. But I promise you it won't work. And then you'll have to destroy them.
Picard: No.
K'Ehleyr: No? Captain, these Klingons are killers. You'll have no choice.
Picard: We shall find another choice. I want options and I want them before we encounter the Klingon ship. Lieutenant [Worf], I'm assigning you to help the Emissary. Dismissed.
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Then there's also the Klingon Ambassador's line from TVH: "There shall be no peace as long as Kirk lives!"
"But what you're talking about is the Movie Era!" Yes, I am. But the hostile, warlike attitude is typical of 23rd Century Klingons in general, certainly Kor and Kang's in TOS, David Gerrold's description of them in 1973 in "The Making of Trek",
and it fits how they're depicted in
Discovery down to a T.
EDIT: I have to say K'Ehleyr is one of my favorite Klingons. We have the same temperament.
And they never,
ever should've fired Ron Jones as a composer. That can't be said enough.