Sorry, Herkimer, my cognitive dissonance won't allow me to see the Trekiverse as being that
simplistic (though you're probably right).
Realistically, it seems to me each empire is probably a slightly warped version of the one next to it, each using a different balance of methods to achieve its goals. As Quark and Garrack put it--likening the Federation to a glass of rootbeer--"It's so bubbly and cloyed... and happy
. And the really scary thing is, if you drink enough of it, you begin to like
it. It's insidious." In short, the Federation wins over its opponents by numbing them into a calm submissive state in a sort of calculated pavlovian mass social conditioning; it's the Disney Channel of galactic empires.
Romulus, on the other hand, doesn't do sweetness or bribes, they just have their agents sneak around in the shadows so you're too scared of punishment to even think about opposing them; in this case, it's the social conditioning usually experienced by fundamentalists who end up policing their own thoughts in fear that they will somehow loose control of their actions and end up being controlled--or worse, confused with--"the enemy."
Klingons buy their empire, apparently, through convoluted family politics, business arrangements and legacy/debts; it's basically an oligarchy, so most of their empire is conditioned to simply accept their collective irrelevance and instead chase fake dreams of glory in some battlefield somewhere, without really thinking about what the battlefield is or who stands to profit from their sacrifice.
The center of all three empires is a single planet--and a single class inhabiting that planet--who rakes in all the spoils from the rest. In the Federation, it's Earth, which has basically become a "paradise" while evidently exporting its varied miseries to the farthest corner of the galaxy, dumping its social/political garbage on planets so worthless it willingly cedes them to hostile empires just for a peace deal. This differs from Romulus only in that it shares the benefits more uniformly among the population of Earth, with off-world humans left to fend for themselves.