^I respectfully disagree, Nightdiamond
. I mean no offense by my statements. I don't think that Cardassia had anything approaching the industry of the Feds, Klingons or Romulans. They had to resort to slave labor, and apparently 12 industrial-sized replicators were enough to get them up and running, indicating a relatively small size (more on that), and a low manufacturing capacity.
I posit that they had relatively few worlds because Bajor is often described as next door to Cardassia and while the Cardassians were a space-faring civilization for centuries, they had not invaded Bajor until the last two generations. Granted, they were less militaristic until the last century ("Chain of Command"), but it seems that mineral-rich, defenseless Bajor would be any empire's first target.
Their military capabilities seemed lacking as well. Benjamin Maxwell's Nebula-class starship was cutting through the Union like a hot knife through butter. I'm not saying that those he could have taken on the Union on his own, but no single Cardassian ship was a match for him (I'd argue that Nebulas are stronger than Galaxy-class ships, BTW).
Combined with my previous arguments about low industry and what-not, I'd say that the only true assets that Cardassia possesses are fine generals and sneaky tactics. This is actually what we see onscreen, too. The best Cardassian villains, Lemec, Garak (yes, he's a villain) and Tain, were all threatening because of their underhanded ways. The worst/most ineffective, Damar, Madred (not a bad character, just ineffective villain) and Evek, never showed any true prowess militarily. Damar is a funny case in that once he became a hero he actually became competent.