Agreed. Though I'm not sure the lack of help from the Federation caused the war, I think tensions just increased more and more between the Klingons and the Federation in the intervening 20-years or so and it just reached a breaking point. It's possible the incident with the Romulans didn't help matters but I doubt it was a contributing factor.
But it was
the destruction of the -C at the outpost that changed relations between the Federation and the Klingons since the ship and her destruction showed that the Federation had honor in them.