Technically, though she'd never be charged for this, Toriel is an out and out TRAITOR to the monsters of the Underground as she purposefully acted against Asgore's decree in trying to intercept and protect the fallen human children (technically everyone who figures out Frisk is a human is too, but Toriel is at the least a 6 time perpetrator, at the same time depending how the other children left her she only "kidnapped" Frisk, and even then she let them go).



Asgore is the suicidal king trapped by politics into doing things he'd rather not (I personally don't think he ever intended to go through with the war, he'd rather suicide by human), Toriel is the traitorous Queen who abandoned her people and King for the children of the Kingdom's "Enemy" humanity (Who hates the king for failing to follow through with his own decree of war and slaughter).



Of course, this is only them at their worst.



Artpixie7 below says Toriel just left him, I personally amend that to her leaving him, twice.



The first after the initial decree, though that probably was to get her own head on straight, but she left him again (or decided to stay gone) when he didn't use the first soul taken to pass through the barrier and gather the others needed (like a coward in her mind).



Someone out there said Asgore is a better Long Term thinker then Toriel who's a great Short Term Planner, which is why they worked well together when they were together, I think you don't see a monster military beyond a few royal guards because "why prepare for a war we'll probably lose, we're behind the humans in technology and they had the advantage even without magic before we were sealed underground".