Which is kind of the point. If it’s a last resort of self-preservation or to prevent an unacceptable alternative outcome, inherent to the choice to engage or endorse large scale violence is the underlying reality of choosing between two evils.
It’s not noble or good. It’s never justified.
Yet in certain situations it may be regarded as necessary.
But a necessary evil is not made good by virtue of its necessity.
And attempts to undermine the absolutism by which large scale violence is inherently unjustifiable, to turn atrocity into Micky Mouse heroism or patriotism, ultimately creates a moral tapestry wherein all atrocities can thus be justified by the relative perspectives of what is good.
So no, there is no measure by which large scale violence transforms into justifiable behavior, under any circumstances.
And a wise society would always regard its adoption as a stain upon its history, irrespective of what other horrors it was brought in to clear out.