Re: Yesterday's Enterprise: How is the Federation Losing So Badly?
One thing that needs to be remembered (but often isn't) in these discussions is that even canonically, in our own 'real' TNG universe, the episode "Aquiel" stated that the last Klingon raid on Federation territory was in 2362, only two years before the Enterprise-D was launched. That's not an alternative universe, that's a solid fact that happened in the 'real' version of Star Trek history.
I tend to view that as a case of over a century of hostilities between the Klingons and the Federation not disappearing overnight. Some Klingon factions couldn't have cared less about the Khitomer Accords and did continue aggression towards the Federation on their own (without being sanctioned by the Empire). Some of these factions may even have been supported by a few members of the Klingon High Council who may have let them off with nothing more than a slap on the wrist.
"Everybody wants to rule the world..."