Remember too this is post-Praxus and so now the Klingon military's hurtin' BADLY for resources prolly, the Klingon military's probably never been weaker, but in the graciousness of the Federation they decided 'No, we're not going to attack them while they are down like this. That would be most dishonorable and we've NEVER win them over then. No, we're gonna use this opportunity to hopefully truly show them we can be the best allies they've ever had if they'd just stop with the paranoia.' xD
Althoguh I'm more a militaristic than a pacifist type (no liberal crap for/from me), Starfleet did the right thing. The Klingons would have went full Kamikaze on the Federation's ass, going down in a blaze of glory. If thez had to die, they'd take the Federation with them, 300 style. Although the war would have resulted in the annihillation of the Klingon race, it would have also left the Federation in ruins, easy prey for the Romulans or the then-upstart Cardassians.