I kept getting the feeling that the Romulans talked a big game, but didn't have the players. The threats were empty because they really were empty, in that they had overtaxed themselves with their century-long infighting, and felt they needed to put on a show of force to avoid the type of scrutiny that would have gotten them in big trouble. That's what the entire alliance with the Duras' was all about, that's why they tried to take over Vulcan, that's why they tried to stay out of the Dominion War until they were dragged in kicking and screaming by Sisko, et cetera.