Modern day warfare is, obviously, different from “glorious” medieval combat.
The Boer War, American Civil War, Russian Japanese War, and several other wars in that time period were fought with machine guns and trenches. That pretty much maximizes casualties. There’s little opportunity for individual heroics and many opportunities to be anonymously killed, possibly because your superiors made the same mistake as they made yesterday, last week, last month, last year, last war. World War I was similar, only this involved many nations, which learned the painful lessons.
World War I also had the Armenian Genocide (which occurred after the Turks won a skirmish against the Allies they thought they would lose; instead of reinforcing their victory they sent troops to murder innocent civilians, and I never once saw a propaganda poster using that as a reason for attacking the Ottoman Empire) and a scandal involving the ANZAC forces who were fighting the Turks. Letters and news reports from the front were being so heavily censored that the civilian population had no idea what horrible conditions their forces were suffering from. (And they were horrendous. The Turkish and ANZAC trenches were less than ten feet away from each other in some places. You literally had to sleep within pistol and grenade range of the enemy.)
Then came the Vietnam War. A nuclear-armed superpower could not defeat “evil” Communist guerillas, because the only way to “win” the war would be to kill vast chunks of the civilian population. South Vietnam was not Communist. I just see it as being a non-Communist dictatorship. The image that sticks in my mind reading about that war had four generals giving an oath of loyalty to the President of South Vietnam. Less than a year later, one of those generals assassinated his superior and took over. Those were the “good guys”.
This was markedly different from the situation in World War II, where people who met every definition of evil were defeated in numerous massive “heroic” battles, such as Kursk, Stalingrad, and D-Day. (Of course, the Allies had to team up with Evil Stalin and dropped two nuclear bombs on Japan, killing many civilians, but we tend to gloss over that.)
Due to the development of the nuclear bomb, there are fewer large scale conflicts. There’s a lot more guerilla wars, where distinguishing between terrorists and civilians is enormously difficult. To get the information needed to achieve some level of victory, you have to team up with bad people, compromising your morals. For instance, tolerating Bashir Assad, dictator of Syria, because he was busy fighting ISIS, a foe that was actually reaching out and touching (and blowing up parts of) the West. Because wars usually involve proxy forces, you have less control over what “your” soldiers are doing. They’re not actually yours.
Also, these days you can outright lie about your enemy (“Iraq supported Al Qaeda”) and throw thousands of your soldiers lives away because… you didn’t like one dictator out of so many.
The sheer number of sides in a conflict make it impossible to root for someone and makes it difficult to even understand a Wikipedia article. I once read about one of the (several) wars involving Syria, Lebonan, and Israel. I decided to group the various combatants into “super factions” to reduce the cognitive load, hoping to keep the number below seven. I don’t remember all the super factions, but they included the Palestinians, the Israelis/South Lebanon Army, Hezbollah/Iran, etc. Now that I had this handy chart, I could understand the war… The war started with one group of Palestinians murdering members of the other group of Palestinians, who retaliated, and at some point one group decided to start murdering Christians as well. My entire “carefully considered” (really extremely naive) super faction technique didn’t survive a single sentence of the Wikipedia article! I wanted to last until the Israelis entered the picture, but… clearly no heroic charges of knights in shining armor, on white horses, saving pretty civilian princesses from enemy soldiers or dragons who aren’t fighting anywhere near civilians, and of course the bad guys, wearing clearly-labeled black hats, are invading your territory and aren’t defending their own land from people they think are evil due to religious propaganda…