Otto Dix, Suicide in the Trenches — big toe on the trigger.
"It was Sam's first view of a battle of men against men, and he did not like it very much. He was glad he could not see the dead face. He wondered what the man's name was, and where he came from; and if he was really evil of heart, or what lies and threats had led him on the long march from his home, and if he would not really rather have stayed there in peace? All in a flash of thought that was quickly driven from his mind."
Helm: Wow, that was harsh. Rogue: Yeah, but you know what's harsher? War in general.
Sgt. Rock had this as a regular theme. The most brutal punishment he could think of one recurring German officer whom he defeated in personal combat was to let him live: "You'll suffer through this war like I have to."
Sin City: Invoked in dialogue — from Wallace, mostly. Marv briefly mentions being in a war and how horrible that experience was. The Villain Protagonist in Rats also vaguely refers to a war. Since it's heavily implied that he's a Nazi war-criminal, it's obvious which one it was.
In Alan Moore's "D.R. & Quinch Get Drafted" for 2000 AD, Waldo's self-described "first exposure to the total insanity that is war" is when he realizes that there aren't any expensive foreign restaurants on the desolate slime jungle planet to which his platoon is being sent to fight on the front line in a very bitter conflict.
Transformers: Wings of Honor also uses this trope, though near the end. For most of the first story, it's more of a action-adventure approach to the war, with the Elite Guard members having fun adventures with quirky or Card Carrying Villains, bar a few instances like when one of the scientists is gunned down, or when the Decepticon leaders have a war meeting, and they're all killed by an unwitting suicide bomber. Then the Sudden Downer Ending hits, where the Special Ops team does rogue, kills almost all the extras and a good chunk of the main cast, and the base is destroyed with very few survivors. In the sequel, the survivors try to take a victory, and though the Big Bad and the traitors are defeated, a new Warlord takes his place, and restarts the war, possibly killing The Hero, and the story ends with the Autobots having to leave the planet as it cannot support them.
While we don't see much of the Civil War in Welcome To The Brothel, the little we do see, combined with its effects on the protagonist, vividly illustrate this trope on a psychological level.
In the Uplifted series the author certainly doesn't gloss over the nastiness of the war, an example would be the Italian sailor who is joking one moment, and cut in half the next by a British airstrike.
Tiberium Wars has graphic, savage, and brutal descriptions of soldiers being shot, stabbed, burned, and vaporized. That's before we get to how completely nasty the battlefields are; one chapter has a group of Nod soldiers slogging through raw sewage, with one soldier getting it in a fresh bullet wound. In one of the latest chapters, we get to see the effects of a full armored assault with Mammoth Tanks from the perspective of the receiving end. Its about as brutally terrifying as one can imagine. In Chapter 17, a Nod officer executes his own wounded to keep them from falling into enemy hands, because he believes they will be tortured and killed. 3 weeks into the war, GDI has managed to fill a stadium with 300 thousand body bags.
Every story in Poké Wars is filled with examples of this trope. The effects of the supercharged Pokémon attacks are described in graphic detail, as well as the feelings of the victim if it's still alive after the hit. The characters' reactions to the more trauma-inducing happenings are just as vividly written.
Skitty screamed both from the pain of the impact and the indescribable agony that arose from the corrupted blood that coursed through her veins, destroying everything they touched. She fought through the pain, struggling to get up before anything could take advantage of her vulnerable state. She tried to get up only to have her legs buckle. Her strength left her as the Ariados venom in her blood began to slowly digest her organs.
She [Solidad] opened her eyes; the scene of her Lapras dying still replayed over and over again in her mind. No matter what she did, she could not erase the sight of Lapras's eyes bursting and her skin scorching as thousands of volts surged through her body, burning her alive.
There's also the fact that the shinigami aren't able/willing to do their jobs of keeping souls in balance and sending the dead from the human world to Soul Society. This means that the entire structure - Soul Society, the human world and the Hollow world of Hueco Mundo - is in danger of collapsing in the not-too distant future. So even if the war goes in favour of the increasingly damaged Resistance, it could yet be for nothing.
Avatar The Last Airbender's fanfic Embers explores this trope even more than orginal cartoon. It's clearly shown what losing their loved ones and costant fight for survival does to characters, especially Child Soldiers. Zuko has more issuses than just being extremly paranoid, Katara snaps after years of represing herself emotionally over lose of her mother and getting Promotion to Parent, Aang lives in denial and it's only thing protecting him from the same fate. Two well-ajusted characters in a main cast seem to be Toph and Sokka, but considering theme of this fics their issues are yet to be shown.
Ace Combat The Equestrian War shows that, as the war with the griffins is progressing, some ponies simply want to quit fighting and live a normal life. Many of them were traumatized by the first major conflict that hit Equestria in hundreds of years.
Live Action TV
As with the Film examples above, several TV series deal with the effects of war on both soldiers and civilians, including Vietnam-era shows China Beach, Tour Of Duty, the pilot episode of The Wonder Years (where Winnie's brother dies) and the modern-day Combat Hospital.
The A-Team: Murdock gives a nice little "war is hell" speech in the episode "The Island".
"War is hell, Wally Gator, isn't it? We know about hell and we know about war, right?"
He was talking to a baby crocodile, and still made it sound deep. Dwight Schultz is just that awesome!
The Crossing: The first scene shows the Continental Army slumping along their line of retreat in bandages, without shoes, bloodied, grimy, sick, and all-in-all in a bad way. Encampment is not where anyone wants to be, and the brutality of battle is quite vividly shown.
Doctor Who: The Last Great Time War is said to be this. In keeping with the show's stance on all violence being bad, it turned the Time Lords into bad guys, forcing the Doctor to kill them all.
Generation Kill: Most of the main cast realizes this after watching a video of what has happened over the course of the show.
MASH: Portrayed generals as bloodthirsty buffoons and emphasised the enemy soldiers' humanity. The military medical setting is ideal for exploring what modern weapons do to human bodies. The doctors themselves are not at home providing medical care, they are overseas working themselves into the ground patching up an endless line of casualties.
The doctors at times serve as mouthpieces for the author's and actor's anti-war views. Hawkeye: "War isn't hell, war is war and hell is hell, and of the two, war is worse." "Why is that?" "...In Hell there are no innocent bystanders." note Barring Persephone, naturally. For instance, when a military bomber pilot comes to the camp after being shot down, he brags at the great time he's having for his term of service. Hawkeye, disgusted at this attitude, invites him to help out during a rush of wounded, which included civilians wounded in a bombing. The pilot is profoundly shaken at the end of the session and Hawkeye apologizes for putting him through that, but there was no damn way he was going to let him return to his duties without learning the consequences of war.
"The worst thing about treating those combat boys from The Great War wasn't that they had their flesh torn; it was that they had their souls torn out. I don't want to look into your eyes someday...and see no spark, no love, no...no life. That would break my heart."
Revolution: Episode 11 has this trope as the premise, with the air strikes systemically wiping out entire rebel camps.
Star Trek: Deep Space Nine: As the only Star Trek series which showed a long time war (the Dominion War) the show often ventured into this with episodes like "Nor the Battle to the Strong" and "The Siege of AR558".
Star Trek: The Next Generation: Introduced The Cardassians during "The Wounded." It gave Miles O'Brien the backstory of having participated in a bloody planet side battle during which one of his best friends was killed.
Star Trek: The Original Series: The episode "A Taste of Armageddon" centered on two planets involved in a clean war, where computers played out virtual battles, and the people on each side were executed to match the results. When the Enterprise gets caught up in it, Kirk destroys the war computers, pointing out that war should be Hell (Invoked Trope), so that people will avoid it. The fear of a real war, scares the planets into peace talks.
Xena: Warrior Princess: For all its campiness, this show never shied away from showing the terrible effect of war.
Dino Attack RPG went into this terrain near the end. Granted, the first few acts involved an over-the-top villain who unleashed Chaos all over the city, characters going on bizarre shenanigans, a campy sub-plot about a psychotic agent who decided to kill everyone with the slightest idealistic views, and a man named French Fries. But near the end, by which point many of the players had grown (the RPG having gone for six years) and their writing improved it got awfully dark for an RPG inspired by a short-lived LEGO Line of all things. Again, this technically depends on the writer, but to name some specific examples:
Atton Rand primarily strove for realism in his later posts starting with the Adventurers' Island arc- which gradually came to be written with this line of thought. He even had the character of Kate Bishop- a young, innocent teenager really not cut out for working on the battlefield- and if anything is ultimately broken by the war.
PeabodySam killed off most of his main cast in the final battle, just to prove that Anyone Can Die. Although he only barely touched upon this in the RPG itself, preferring to write a more Bittersweet Ending in comparison to Atton's Downer Ending, he has confirmed that a handful of the survivors will suffer from PTSD, depression, or other such problems in the years following the war.
that guy from that show exemplified this trope through numerous characters he introduced. Pharisee was forever hardened by his exposure to the more horrible acts committed during the war between the Crusaders and Black Falcons. Solomon Koplowitz was a philosophy professor turned Knight in Sour Armor after witnessing firsthand the horrors of war between ninja and samurai. Carl Lutsky was driven to insanity in the days after finding himself promoted to the position of commander in the Dino Attack war.
Most of the games in The World of Darkness tend to glamorize violence, intentionally or not. Wraith The Oblivion, on the other hand...doesn't. It really hammers home the horrific, pointless nature of war, and the two books dealing with the World Wars (The Great War and especiallyGhosts of the Shoah) may be the bleakest things ever written by White Wolf.
Works by Stuart Slade, such as The Big One and The Salvation War, make a point of portraying exactly how horrible modern military weapons technology can be, mostly as a reaction to how underestimated or cavalierly such weapons often get treated in much fiction. It helps that the author is a professional military analyst, and he shows his work by refusing to shy away from excruciatingly detailing exactly what modern weapons — from the "lowly" assault rifle to weapons of mass destruction — can do to people. In The Salvation War: Armageddon, for example, the forces of Hell learn first hand the horror of modern, mechanized total war. One of them even remarks that the battlefield they were fighting on was a human-made hell. Quite a rude awakening for the army in question, especially as they were at bronze age levels of technology.
In the sequel to The Salvation War, Pantheocide, we get "treated" to the angelic army being hit with a nuclear initiation. The description of the results is chilling..
Kickassia presents a humorous version of this trope, with various incidents happening during the 'war':
In the end, when all is said and done... Rob realizes that he left the lens cap on.
In Spectral Shadows we have Harrison James, who would wake up in the middle of the night from nightmares, resulting in all the horrors he witnessed as a soldier during Chikyu's Second Great War.
Universal Cartoon Studios productions
Wing Commander Academy - As much as could be portrayed in a 1990s Saturday morning cartoon, the series is not at all shy about the death and occasional moral ambiguity of war, on both sides.
Probably the best episode for this is one where a kilrathi pilot crashlands on a paradise planet and holds the female doctor there hostage. She seems to have been taken over with Stockholm syndrome when Blair and Maniac find her, and eventually after stopping them from fighting one another she convinces them to let the Kilrathi leave, after having him promise not to reveal the beautiful planet's location so it may survive the war unscathed. Blair and Maniac agree to let him go, and he flies off...then they find notes implying that when she was treating his wounds she was also experimenting on him, and has bioengineered him without his knowledge into being a walking viral factory, who will die upon returning to Kilrah and spread the disease throughout their homeworld, wiping out the entire Kilrathi race. Blair and even Maniac call her out on this insane plan, then take off to shoot him down. They both feel pretty crappy about it afterwards.
Avatar The Last Airbender explores the prolonged effects of Imperialism, foreign occupation, and genocide as much as it can while still being viewable for children. One episode has the commander of an Earth Kingdom fortress show our heroes an infirmary, and then mentions that those soldiers are the lucky ones, because they came back. Everybody has their lives affected by the war: the main character is the last of his kind because every single one of his people were massacred a hundred years earlier, and two of his companions lost their mother to a raid. They also meet many people whose villages were burned to the ground, with most of them losing their families in the process. One even blows up a dam to try and clear out Fire Nation soldiers, knowing that the flood will kill innocent civilians as well. The heroes at one point find a refugee camp, where people are left with few possessions and in cramped conditions, trying to buy passage into Ba Sing Se, one of the few safe cities. They even meet a woman who was taken from her village simply because she was a waterbender, who then spent years learning how to manipulate the blood in people's bodies and now blindly seeks revenge.
Star Wars: The Clone Wars does this a lot to contrast itself to the first, Tartakosky series which was "War Is Glorious". First shown in Rookies where a group of clones tries to retake an outpost...only two survive besides Rex and Cody. Its really hammered in hard during the Kaminoian Invasion where 99, a defective Clone is killed. And finally in the latest Umbara Arc? Its so hellish (and the Jedi General is evil since he was defecting), the Clones are tricked to killing each other.