The Great War differed most significantly from previous European
conflicts due to which of the following?
A The notion of civilians as combatants
B The ideology of war as noble and good
The involvement of nationalistic movements
C
D
The complications of a regional alliance system

B The ideology of war as noble and good

...is your best answer.

Explanation:

Previously, wars was seen as something that was noble, and even elite. However, with the introduction of trench warfare, and the new brought horrors of what the advancement of humanity that was brought to the war zone, it  brought about the end of the "noble part" of war. Not only was there technological advancement in weaponary and delivery of weaponary, but also the impact each and everyone has. Gone are the days in which you must "look into the white of [your enemies] eyes". Whether in the expanse of no-man's land, or shivering in the trenches that may be the graves of young dreams, soldiers are frightened by the new idea of death, one in which, the horrors of war settle, the truth spews out, the stories they told were inflated lies, and that death was imminent & near. Nowhere was found the stories of noble acts, or that the distant memories of goodness was found. The war changed people's opinion of glory, and brought them to the reality, that glory comes not from war, not from death, and that there is no such glory on the battlefield. No matter how much one wins, it will always be a pyrrhic victory, or a bloody defeat for every single soldier from wars starting from the Great War and onward, as their humanity is slowly ripped away from them.

~

i think it would be c.

hope i'm correct

explanation: