Pendulum War

During The War Sequence, well, there's a war going on. This means that a lot of people are eagerly going at it at once -- something that is extraordinarily difficult to film in any satisfactory manner. There's just so much going on at any given moment, and the reader or viewer or player can only see a small part of the action. There's also the fact that many stories with such a sequence are essentially heroic stories -- the dehumanization and intermittent back-and-forth of a battle doesn't really fit so well into the theme of such a tale.

Because of this, many battle sequences in works of fiction seem to go in one of two directions -- either the Redshirt Army is getting clobbered, or the Evil Minions are. It almost seems like armies in television, movies, or games can only be in one of these two extremes -- there are never intermittent stalemates or indecisive exchanges.

The actions of the heroes, furthermore, are often disproportionate to their actual effect in the battle. No random extra achieves anything in the battle; only named characters can be militarily useful. Of course, given the power of many heroic or villainous characters, this is somewhat more believable -- especially if the series is Fantasy or Science Fiction, where a single individual may just have the power to destroy entire cities with a thought.

In any case, this effect will swing this pendulum back and forth; usually, until The Cavalry arrives, scenes of carnage and tragedy will dominate, until they crest the hill and suddenly the Evil Minions who just moments ago were rampaging unchecked are now fleeing in disorder.

This trope has some basis in fact -- many real-life battles are decided on morale and momentum -- but it still sometimes feels vaguely manipulative to base the fates of so many on the actions of so few, in such a literal sense.

One-sided encounters are perfectly reasonable when those involved have radically disparate technology levels, resources, and/or training.

See also: Redshirt Army, Evil Minions, Conservation of Ninjitsu, Only I Can Kill Him!

Anime and Manga

 * Largely averted in Robotech. Even the winning side in the battles takes heavy losses, and Earth manages to do some damage even when using a few early space weapons against the massive and technologically superior Zentraedi fleet.
 * Averted in Legend of the Galactic Heroes, where many of the larger pitched battles are brutal stalemates with millions of casualties on each side, no matter who wins in the end. The camera frequently switches to the gory deaths of Mooks from both sides to highlight the horrific human suffering caused by war. These scenes tend to be filler for the narrator's Author Tracts bemoaning the futility and hypocrisy of jingoism and violence.
 * The Battle of Mahora in Mahou Sensei Negima was fairly even between the students and robots...until the giant demon mechs and robots with gatling guns that fire time displacement bullets showed up. Things quickly went downhill from there.
 * In Turn 11 of Code Geass R2, Zero turned the tide against the Chinese Federation by combining the introduction of a new mecha, Shinkirou, with a Xanatos Gambit that caused the country's population to rise up. Partially subverted in Turn 18 with Kallen and her new Super Prototype. She started to pick off enemy units and could probably have wiped out the entire Britannian army, given enough time, but the battle actually ended in a more inconclusive fashion for both sides thanks to the unexpected use of a certain weapon. On the other hand, a straightforward example happened in Turn 22, after Suzaku had received a similarly powerful upgrade and was able to destroy a small army of Knightmares in the span of a few minutes.
 * When the titular guild of Fairy Tail breaks into the Phantom guild they completely decimate all of the opponents forces, and it's seems that despite being a magic guild none of the members of Phantom but the highest are actually using any magic. Then, Master Makarov gets his magic drained (which is stated to mean "their battle strength is reduced by half"), and the Phantom guild-members--who are still not using any magic--somehow start fighting off the Fairy Tail members and Erza decides they need to retreat.
 * In One Piece, during the battle of the Whitebeard Pirates and their allies against the Marines at Marineford, the pirates just charged forward only being slowed down and anything important was being done by the high-ranked pirates and officers, but the deaths of a small number of many of their forces

Film

 * Troy oscillates wildly between Trojans beating the snot out of the Greeks (when Achilles isn't around) and Greeks annihilating the Trojans (when Achilles is around).
 * The battle scenes in Braveheart are a prime example of this trope: the English and Scottish extras don't actually get to kill each other. Only Mel Gibson's character and other Scot heroes get screentime to do mass slaughter. Even in the last battle where the Scots lose, there are only a few shots of Scottish soldiers getting hit with arrows. The rest of the scene is Mel Gibson wading through English grunts.
 * The Army of Darkness, probably about a thousand zombies, were held off by sixty men until reinforcements came from Scotland. Bruce Campbell fought on both sides.
 * In 28 Days Later the 10 men making up the whole of England's defenses are only really able to hold off the Zombie Apocalypse because of their predecessors having thinned the ranks a little, and most likely added to them as well. The battles we see are, as can be expected in the epic clash of Hordes of Stupid Infected versus Nine Guys With Guns, in the humans' favour until plot requires them to be otherwise.
 * The film version of Battle of the Bulge is exactly like this. Either the Germans are completely succeeding or they aren't. In a battle that included over 800,000 soldiers, the battle was completely one-sided. Throughout most of the film, the Germans are succeeding in every single thing they attempt. Weather, machinery, and even the attitudes of the American leaders are on the side of the Germans almost to the point of being comical. At one point, a general even chastises a lieutenant colonel for suggesting that the Germans may intend to attack. When they do attack, the Americans are surprised. The only thing that turned the tide on the Germans was that they ran out of fuel. At that point, they completely gave up, despite still having weapons and ammunition and the ability to fight.
 * Saving Private Ryan averts this: the opening Omaha Beach sequence is one of the most realistic and unglamorous portrayals of war, ever, in a Hollywood film. The winning side suffers great casualties almost from the start, and Captain Miller, the film's "hero", is just another insignificant soldier. Same with the final battle: long and hard, with the winning side suffering great casualties, and the victory is due to the collective efforts of the Ensemble Cast.
 * The Star Wars films largely avert this, as named characters are usually essential for victory but random soldiers on both sides score most of the kills. That said, the battle of Naboo in The Phantom Menace is completely a One Sided Battle. The good guys are getting creamed, and then
 * Battle: Los Angeles features a surprise Alien attack, then the Marines get sent in with air support and seem to be coming out on top.

Music

 * "8th Of November" by Big & Rich. Features the battle fought on 11/08/1965 called "Operation Hump", referred to in the Real Life folder.

Literature

 * Older Than Feudalism: In Homer's The Iliad the Trojans beat the snot out of the Greeks (when Achilles isn't around), the Greeks annihilating the Trojans (when Achilles is around).
 * In the The Lord of the Rings books (and movies), Gondor is getting badly clobbered until Rohan's cavalry arrives. In the movies, the conflict is presented by scenes of desperate struggle within the city walls and civilians fleeing screaming in terror -- with emotive music playing in the background, of course. This also occurs in The Hobbit; the Battle of Five Armies swings back and forth, back and forth, from extreme to extreme. However, the latter example is also a subversion, in that Bilbo, the viewpoint character of the book, is knocked out early in the battle and only comes to once it's all over.
 * Gondor is not badly clobbered in the books. Gondor is beaten back by huge hordes of orcs (and managed to rack up awesome kill ratios - 10 dead orcs for every dad man), but is hardly clobbered.
 * A siege that breaks through the outer walls of their capital city seems pretty clobbered. One character even remarks that they're like a child trying to threaten a knight. If Sauron had known that they didn't really have the One Ring, they would have been as good as dead.
 * The siege barely broke through the walls in the book; there were never orcs and trolls rampaging through the streets the way they did in the movie. The only enemy to enter the city is the Witch-King of Angmar, and he's only there for maybe a minute. Further, the line about being a "child trying to threaten a knight" is when they are attempting their diversionary action to distract Sauron from Frodo, after the siege has been broken.
 * Of course, assuming that Gondor actually WASN'T being clobbered, that would mean that the Reinforcements weren't as needed as they were made out to be. Which going by the theme of the book, rather unlikely. Of course, Gondor still had at least 1 Rigged Hero left, and all Mordor had was a bunch of Elite Mooks, Hordes of Even More Useless Mooks and The Dragon that never does anything useful. So maybe Gondor could of withstood it afterall.
 * It's also worth noting that the design of Minas Tirith meant it could actually survive surrendering not only the city's outer wall, but five of the inner walls (and the rings of city contained between them) as well . Provided the siege was eventually lifted, anyway.
 * The Redwall book series is notorious for this. No matter how much the vermin army is built up, the actual fighting is almost always in favor of the good guys. Even if they're pacifist churchmice. Outnumbered 1,000 to 1.
 * They usually have the advantage of terrain, as well. For the Redwall sieges, anyway.
 * Both used and averted in the Gaunt's Ghosts series; the titular Ghosts are usually either handing the assorted minions of Chaos their mutated Chaotic rears, or they're royally getting their own kicked. Even in the battles they win, they usually suffer some casualties.
 * Justified by the wildly divergent nature of Chaos troops. Most Chaos forces are barely-controlled rabble, generally undisciplined and unskilled, with poor structure, no squad support weapons, and "armor" an average dune buggy could beat in a fight, if they have armor at all. On the other hand, elite Chaos troops are hardened fanatics, literally trained from hell, with plenty of heavy weapons, Chaos Leman Russes and Baneblades, and often backup from Chaos Space Marines, alien mercenaries, or other Super Soldiers. There isn't a whole lot of middle ground between the crap and the elites.

Mythology

 * There's a high-numbers war in the Mahabaratha, but all the interesting stories about the main characters (on both sides) singlehandedly or in small groups breaking through formations made of hundreds of random soldiers. In fact, there's even a "hero" ranking reserved for warriors who can singlehandedly kill a thousand or so "normal" soldiers. Needless to say, main characters on both sides (and their near family) tend to do that.
 * Arthurian legend does this often, although just as often there aren't any armies, just little clumps of knights. Check out Malory for good examples of the trope actually in action. Geoffrey of Monmouth, despite his habit of making history up, was actually fairly reasonable about battles.
 * Remember Chanson de Roland: In Roland's final battle, he slays thousands of enemies before perishing from blowing his horn too hard.

Tabletop Games

 * A variation in Warhammer and Warhammer 40000. Any given army is unstoppable, if not invincible, in its own Sourcebook. Consequently, if it appears in any other Codex, it's getting stomped.
 * This can be justified to a degree: how many people do you know of brag about their loses?
 * Inverted by the imperial guard 3.5 codex. The only fight in there is guard on guard. And it's inconclusive.

Video Games

 * The Dynasty Warriors games take this trope to its logical extreme -- only the player's characters can actually score military victories. The various Redshirts on the field are just there to rack up your kill count; they mostly just mill around and certainly have no chance on their own against you.
 * Except on "Chaos Mode" in some games, where it's inverted. All it takes to kill the player is (for example, in Warriors Orochi) 3~5 arrows... And let's not get started about how "enraged" (an in-game boss status, where the boss is juiced up with red Battle Aura. You don't wanna take a hit from it, trust me.) can do horrible things to you.
 * The Empires revision of 6 now allows allies to finish battles.
 * Parasite Eve:During the second game Aya Brea finds herself witness to one of these when surrounded by dozens of ANMC Golems, armored monsters equipped with energy swords. Suddenlly The Cavalry arrives in the form of United States Marines, who proceed to utterly annihilate the entire horde of monsters in under a minute with liberal application of explosives and machine gun fire. It's so one sided.
 * This is explained pretty thoroughly in the game. The creator of the Golems found them to be quite difficult to control and reasoned that it would be best to only arm them with swords (the ones with grenade launchers that you meet in game made an unauthorized trip to the armory after everything went to hell). The reason he gave them swords is discussed near the end: If they ever revolted a small band of people armed with automatic weapons could easily suppress them. The fact that The Marines slaughter them with M249s is pretty reasonable.
 * In Valkyria Chronicles, most of the battles between Gallia's and The Empire's ends with the Gallian army getting their asses handed to them. This goes in the other direction once Squad 7 arrives on the scene.
 * Ace Combat Zero had Operation: Battleaxe (the 10th mission, Mayhem), where the allied air forces fought against the Belkan Air Force over the Round Table. Initially it became one sided in favor of the Belkans with almost the allies shot down. Then the Galm Team (consisting of two fighters) comes and turned the tide of battle. It was actually because of this battle that the Belkans knew they were going to lose.
 * Princess Waltz is the One Girl Army variant of this trope, constantly curp-stomping one another until one side is Out Gambited
 * The final battle against the Sith Fleet in Knights of the Old Republic turns out this way if you redeem or kill  - but if you choose the Dark Side path, it rapidly goes from "Sith victory in progress" to "complete annihilation of the Republic fleet". This is due to.

Western Animation

 * Star Wars: Clone Wars seems to have a pattern: First the big huge armies are fighting and the good guys are winning, next some character working for the Sith comes in and is able to completely turn the tide of the battle with just his/her presence, then a Jedi character comes in and flips it over again (unless the Federation's side has Grievous, then he'll beat the Jedi and it remains one-sided).
 * Teen Titans: In the penultimate episode "Titans Together", the final battle starts with a ragtag group of heroes who have escaped the Brotherhood's grasp putting up a surprisingly good fight, becomes one-sided when reinforcements show up, and (broken up by two brief scenes of the Quirky Miniboss Squad trying to turn the tide) becomes even more one-sided when the Titans captured in the previous episode are unfrozen, in spite of the fact that this should only bring their numbers up to about equal.

Real Life

 * The Korean War. First the North Koreans pushed the South Koreans all the way back to Pusan. Then the South and their allies push the Northern forces back to the Yalu River. Then the North and their allies pushed back.
 * The Iran-Iraq War. Both sides push the other back and forth inflicting heavy casualties on both of their troops while doing so.
 * The 1973 October War on the Egyptian front at least. Egyptian success in Operation Badr followed by the successful Israeli counteroffensive across the Suez.
 * A recognizable theme in warfare among Europeans and European inspired military cultures. One side will find some technical advantage and roll over it's opponents for a time. However all occidental armies were formed in an environment so similar that it is impossible to find a technique that is incomprehensible; for instance Horse Archer s needed a culture that was Born in the Saddle but Panzers were made by a culture similar enough to Britain, US, and Russia that they could be countered or copied sooner or later. As a result at some time there comes a point where the advantage of experience added to technical knowledge in the superior side does not make up for losses in officers, while their victims have gained enough experience to compete. Furthermore the originally successful power frightens others into taking the side of the loser to preserve the Balance of Power. Examples of this are the Napoleonic Wars, The American Civil War, the Great Northern War, and World War II.