The Federation is an odd government. It asserts territorial control without asserting sovereignty over that territory.
This leads to some unusual situations like the Nausicaan and Orion homeworlds being inside the Federation but not in the Federation.
In those cases, a government like the Klingon Empire would say "we own your planet and there's nothing you can do about it," the Federation says "we don't own your planet, but we own everything around it and if you shape up you can join us."
I'm not sure this sort of governance would actually function in the face of hostiles inside its borders, TBH. But nobody ever claimed Star Trek was realistic.
Well, yeah. But then again, space is also three dimensional so I don't see any of the empires functioning very well with traditional notions of sovereignty.
And with the weapons and replicators present, once a culture has that technology (and you can replicate a replicator or there'd be no self-replicating mines), I'd think traditional empires like the Klingons or Romulans would be very difficult as subjugating a world with replicators is nigh impossible. So I'd be inclined to think that the bigger you are and the tighter control you maintain, the weaker you are... and there's little incentive to control planets anyway except for dilithium and latinum. And the big need for dilithium is in controlling the space ways.
The net result being, controlling boundaries would be more important than controlling worlds and controlling worlds is mainly about ship fuel to control spaceways. And controlling spaceways absolutely is difficult. Romulans and Cardassians therefore rely on controlling information and blackmail. The Federation tries to control spaceways and its strength comes from not having to expend much in the way of dilithium on policing, while having nearly limitless replicator resources. Meanwhile, the Klingons' approach always struck me as... well... making them weaker and weaker with each military action. Plundering is irrelevant with replicators. Recrystalizing dilithium makes having more dilithium more of a time advantage than an overall advantage.
I'm not sure that the Klingon style wars can be regarded as a net gain at all. It's sport at best, an expensive sport. As conquering planets never makes you stronger for doing so, only weaker. The only real advantage probably comes from stealing technology, which is I suppose how the Klingons get by, being basically a tougher and smarter version of the Pakleds. But I can't imagine the bulk of their efforts pay off and so they're hindering themselves.