WWI still didn't have total war or deliberate destruction of entire cities using aircraft. The bombing of Guernica in 1937 was considered shocking at the time.
WWI eventually defined total war, and no doubt its legacy was the primary reason France just surrendered to the Germans in 1941. The entire population had simply had enough.
> Some 9 to 10 million combatants on both sides are estimated to have died during World War I, along with an estimated 6.6 million civilians.[citation needed] The civilian casualty ratio in World War I is therefore approximately 2:3 or 40%. Most of the civilian fatalities were due to famine or Spanish flu rather than military action. The relatively low ratio of civilian casualties in this war is due to the fact that the front lines on the main battlefront, the Western Front, were static for most of the war, so that civilians were able to avoid the combat zones.
> According to most sources, World War II was the most lethal war in world history, with some 70 million killed in six years. The civilian to combatant fatality ratio in World War II lies somewhere between 3:2 and 2:1, or from 60% to 67%.
I found out recently that "Spanish Flu" is so called because all the countries fighting in the war censored any mention of it happening in their camps, where it almost certainly originated.
From wikipedia:
"To maintain morale, wartime censors minimized early reports of illness and mortality in Germany, Britain, France, and the United States;[9][10] but papers were free to report the epidemic's effects in neutral Spain (such as the grave illness of King Alfonso XIII),[11] creating a false impression of Spain as especially hard hit[12]—thus the pandemic's nickname Spanish flu."
and
Investigative work by a British team led by virologist John Oxford[15] of St Bartholomew's Hospital and the Royal London Hospital identified a major troop staging and hospital camp in Étaples, France, as almost certainly being the center of the 1918 flu pandemic. A significant precursor virus, harbored in birds, mutated to pigs that were kept near the front.[16]
Er, France surrendered in mid-1940, and they surrendered because they were not able to mount a defence to Blitzkreig, had lost a large proportion of allied forces to the overrun (including the BEF at Dunkirk) and decided to surrender Paris and survive rather than risk it being obliterated in urban warfare. Given what happened to Stalingrad that doesn't look like a bad choice.
In some ways WW2 was the last of the wars of colonisation to be attempted. Assert racial superiority, a need for land, define the "natives" already occupying it as subhuman, invade and kill them, extract resources and colonise. This time in Russia since Africa was already taken and the Americas already liberated.
WWI eventually defined total war, and no doubt its legacy was the primary reason France just surrendered to the Germans in 1941. The entire population had simply had enough.
Hell, Sherman was fighting total war in 1864.