The Overlord wrote:
What do you think likely happened to Cardassia Union after the Dominion War?
Cardassians would be stripped of the majority of their territory. Certainly any "colonies" with indigenous populations would be evacuated of the resident Cardassians, and should the natives be primitive, Cardassian technology and structures would be removed. Any star systems/planets in previously disputed areas would be transferred to non-Cardassian parties. Chakotay's people would finally get their planet back, others too. There would be legitimate need for the Cardassians to retain small patrol starships, but their medium and heavy warships would be confiscated. Colonies established on uninhabited world might remain the territory of the Cardassians.
They never really were threatening until the Dominion propped them up.
Picard (from Journey's End): "... the last war caused massive destruction and cost millions of lives
. Don't send our two peoples back down that same path again."
While you could claim that was very one sided, that the vast majority of deaths were Cardassians, and Starfleet was just hosing down civilian populations with phaser fire from orbit, it sounds more like the Cardassians had a large military that could dish it up, as well as take it.
In The Wounded, nearly a year after the end of the war, Vice Admiral Haden said "... Federation is not prepared for a new sustained conflict."
Benjamin Maxwell's Nebula-class starship was cutting through the Union like a hot knife through butter.
Maxwell destroyed one supply depot, one supply ship and a single warship.