The high amount of victims causing internal opposition to the war IS a self-imposed restriction. The war was too distasteful, so they stopped. Their civilian populations (and/or religious leaders, etc.) were unable to understand or accept the brutal realities of what a war actually is.

In the US especially, we think our wars will be "John Wayne movies." "It'll all be over by Christmas," or some other such thinking. That was the general attitude at the start of the Civil War. But, when it wasn't that easy, both sides just got angrier and more determined, and both were committed to seeing it through. In WWI, we showed up late, and provided enough "umph" to push Germany over the edge and quit. Gee, that was simple enough, huh? "Wars all go like this." In WWII, we were really, really angry at Japan, and determined to see it to the end. (My mother would seeth with anger even 30 years later when she would talk about it.) We were committed to see it through, and the government was supported, and expected to "do what it took." Horror and carnage? Fine. Are we beating the bastards? Good!

In Vietnam, Johnson would use bombing, then pause and extend an invitation to Hanoi to negotiate. When they refused, he would repeat that...bomb, then stop (as a gesture of goodwill) and offer to negotiate. In contrast, Nixon started bombing, and told Hanoi he would stop only when they started negotiating. That got them to the table. We signed a peace deal that preserved South Vietnam (victory...that was our objective) and Nixon made it very clear that if the agreement was violated, he would resume bombing. Then, Ford came in and publicly declared we were sick of war, and would never return. Hanoi knew a green light when they saw it. No more South Vietnam.

My mother used to say, "If you get angry, stay angry, and don't stop until you get what you were after." (And 30 years later, she pretty much could not stop being angry...) IF your country wants a fight, but is only prepared to "go until Christmas," or some other nonsense, then expect to lose.