system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] Why isn't the threat of mutually assured destruction able to stop powers in the Alpha Quadrant from going to war?

The Federation, the Klingons, the Romulans, and a bunch of other major Alpha Quadrant powers have the capability to produce tri-cobalt warheads. One tri-cobalt warhead is capable of making a star go supernova and also destroy its surrounding systems. This is like the "nuke" of the 24th century, yet MAD is essentially non-existent, and because of that wars between major powers is a common occurance.
gpt
The thing is, that's not mutually assured destruction.

During the Cold War, the US and Russia could each have wiped out every one of the opponents meaningful population centers in a single move. The other would have just enough time to register the incoming missiles and launch back. But consider this: What if instead of fighting the US, Russia's primary opponent had been the British Empire at the height of their expansion, with military facilities in every territory. 

They could do a lot of damage, but they could never count on destroying every vestige of the British government. This would make for an asymmetry that breaks the Prisoner's Dilemma. 

Similarly, the Romulans or the Klingons could destroy Earth, and in return, have Romulus or Quo'nos destroyed. But the coordination it would take to have warbirds lying in wait around every star that the Federation has a colony at would be *staggering*. 

There is a limited form of MAD in play - neither side is willing to be the first one to use the tri-cobalt option,  because it *will* bring retaliation in kind. But since neither side could wipe out the other at once, conventional warfare remains on the table, rather than merely the proxy war you see between nations of Earth using nuclear weapons.

TL;DR: Tri-Cobalt warheads are terrifying, but they're still not capable of *assuring* civilization-wide destruction. There's just too much civilization.