I think that had the Federation intervened regarding Bajor, the Cardassians would have gone to war, become a third-rate power because Starfleet would have dealt them a serious blow. A pathetic treaty would have been imposed on the Cardassians when they surrendered...it could make for an interesting MyrU story idea.
One of the (many) things that bother me with how the Union has been portrayed in the Star Trek Universe is precisely relates to the above, namely Cardassia as a third or even Forth rate power. After all, the Union is (or rather was) one of the big four of the Alpha and Beta Quadrants and has been described as the leading military force in the AQ. I therefore would have reason to believe that a war between Cardassia and the UFP would not go down as easily as is outlined above, Starfleet might win it but they would know that they had been in a real war.
With regards to the Occupation of Bajor, why does anyone seriously think that the Federation would move to liberate the Bajorian people? They are allies with the Klingon Empire which has conquered dozens of worlds and placed millions into slavery. Not to mention the RSE which made slaves out of their own kith and kin. I do detect a certain double standard here but then the Klingons are of course honorable so that makes it all right
Cardassia only become a third rate power after the Klingons launched their cowardly sneak attack on the Union and destroyed the Cardassian's industrial capacities, leaving millions on the brink of starvation and disease as well as destroying transport ships and outposts often killing over a quarter of a million Cardassians in one go.
It's no wonder that Dukat made the Devil's deal with the Dominion, it was the only way he saw to save his people. ( I doubt that Dukat would have made that choice had he but known that it was a founder who lead the Klingon assault on the Cardassians, although Growon's paranoia and stupidly played a massive role as well.).
The Klingons also helped to destroy the gains made by the Cardassian Revolution of 2372; namely a free and democratic Union that would have made peace with Bajor and the Federation as well as resolving the Maquis situation in a reasonable manner. Instead the Klingons had their dammiable war which gave the acien regime
the opportunity to return to power and as a result unleashed the Dominion war on the AQ.
Therefore I would argue that the Klingon Empire played a massive role in starting the war and should have been held to account for it.
Here endth the rant...