I qualified that with wars with “Civilized” oppponenents. One of the reasons the white indian conflictys were so horrible was the lack of either side following the military conventions of the day.
But it was mutual. Google Gnadenhutten
There was a certain need to instruct the Indians on what it meant to go to war. That was the purpose of the Ranger raids in the French and Indian war. Also the purpose of the Sullivan expedition in the American Revolution. It worked. The Indians were part of the forces of France and Britain, nominally civilized.
The prison ships used by the British to murder Continental POWs through sickness also indicate less than the usual care for civilized standards. By contrast, Gen Washington impressed on his officers that captured British soldiers should be given every care, to avoid inflaming passions that would prevent an early peace.
There was a certain disappointment in US Army commanders during the War of the Rebellion when so called confederate snipers used exploding bullets, or when Gen. Wheeler put infernal devices on roads. Certainly Gen. Sherman felt freed of the normal practice of keeping rebel prisoners safe, and quite publicly put them to work clearing the roads of mines. That order quickly ended the practice of planting infernal devices, and probably saved many southern civilian lives that would have be killed by Wheeler’s mines.