All wars go through progressive cycles of increasing brutality. The longer a war grinds on, the more brutal it becomes.
The American Civil War began with dress parades; it ended with corn cribs and hog pens in Georgia and the Shenandoah Valley being military targets.
World War 1 saw a “Christmas Truce” in 1914. By 1918, the use of every kind of gas was practiced on both sides.
World War 2 had an early phase of the deliberate sparing of hospital ships by both sides. By 1943, they were being sunk. The bombing of Warsaw and Rotterdam were considered barbaric. The firebombing of Dresden and Tokyo were simply the continuation of military policy.
“It is well that war is so terrible. We should grow too fond of it.” - Robert E. Lee