Two groups have been locked in a Forever War for a long, long time. Then, a third party (like The Hero) comes along and wants something from both of them. But first, he has to play the peacemaker and stop the senseless bloodshed for them to work together with each other, and with him.
Setting the stage can vary in method: sometimes all that's needed is a Patrick Stewart Speech to invoke a Heel Realization in the groups. In more cynical works, the hero could outright demand a ceasefire and threaten to kick both sides' asses unless they throw down their weapons and talk it out. Success usually results in a very, very awkward but hopefully honest (just how awkward and honest will depend on whether Ontological Inertia factors in or not) handshake between the two leaders and a Moment of Awesome for The Hero.
Compare Young Love Versus Old Hate, which can overlap with this (cf. Romeo and Juliet) but not necessarily, Third-Party Peacekeeper, when a mutual friend tries to smooth things over, and Velvet Revolution, when a conflict that started off violently immediately winds down peacefully. Contrast Mediation Backfire.
- The main character's goal in Naruto is finding a peaceful resolution to the ancient ideological conflict between two dominant ninja clans, Uchiha and Senju.
- In the Skypiea arc of One Piece, the centuries-long war between the natives of Skypiea and the tribal Shandians finally reaches a peaceful resolution after God Eneru nearly destroys everything and is defeated by Luffy. Luffy wasn't actually trying to do this, though; it was just a consequence of his actions.
- The war between the Tribes of Light and Shadow in Words Worth broke out over the shattering of the eponymous magical tablet and is ultimately resolved by a child descending from both Tribes, who reassembles the tablet and interprets its inscriptions.
- Asterix in the Corsica album. As the Corsican chief stated: "Defeating the Romans is nothing special, but making two foes reconcile definitely is!" (paraphrased)
- In The Icemark Chronicles, Thirrin successfully forms an alliance between the Icemark and the vampires, despite the fact that the Vampire King and Queen have been their enemies for over a thousand years.
- In Terry Pratchett's Thud!, it turns out that the most infamous event in the thousand-year war between dwarves and trolls started with a huge misunderstanding. The dwarves said that trolls ambushed them at Koom Valley, the trolls say the dwarves ambushed them. In reality, a sudden fog that fell over what was supposed to be a peace-talk lead to panic on both sides, and the ensuing battle was interrupted by a flash flood that wiped out everyone left. The discovery of a secret message from B'hrian Bloodaxe, former king of the dwarves, and the clumsy attempts by some extremist dwarves to cover it up leads to the truth finally coming out and the beginning of a true peace between trolls and dwarves.
- Star Trek: The Original Series episode "A Taste of Armageddon." The planets Eminiar 7 and Vendikar have been at war for 500 years. However, for most of this time, the conflict has been completely simulated on computers. When the computers tell the inhabitants of the planets that they've been "killed", they obediently file into disintegration chambers and are destroyed. Captain Kirk sabotages the computers running the conflict after they target his ship, which will force the two planets to fight their war for real if they want to continue. He figures that the horror of possible planetary obliteration will cause the two populations to seek peace instead. He turns out to be right - the planets do start negotiating.
- In the Star Trek: Voyager episode "Alliances", Captain Janeway tries to act as this between the Kazon and their former rulers, the Trabe. Unfortunately, the Trabe can't resist an opportunity to take out the major clan leaders.
- On Star Trek: Enterprise, Captain Archer plays this for the Vulcans, Andorians, and Tellarites. It ends up laying the groundwork for The Federation.
- The eponymous station in Babylon 5 starts as an attempt to create a Fictional United Nations to peacefully mediate disputes between the various alien species. When Earth itself falls to a Shadow-backed dictator, they're paid back for their efforts when the long-warring Narns and Centauri take the lead in getting the other races to back the forces loyal to the former democratic regime.
- On one episode of M*A*S*H, Hawkeye, incensed at learning that due to a regulation change, he was going to be stationed in Korea for longer than he thought, drives to the Peace Talks in Panmunjom on a whim, bluffs his way into the tents where the talks themselves are being held, and makes an impassioned plea for the two sides to reconcile. It doesn't work, but he manages to avoid getting busted for it, and when he gets back to camp, the rest of the outfit throws a party in his honor.
- What Saint Lin did in Embers in the Dusk with the warring lizardmen empires on Avernus, the Saurus and the Skinks, by creating a peace treaty. Their feud has been going on for longer than humanity has existed, and is said to have started shortly after the War in Heaven.
- Mage: The Ascension's concluding book, Ascension, allows players the opportunity to bring a peaceful end to the conflict between the Technocracy and the Traditions, with a little help from the Void Engineer master Tychoides. At this time, the two factions are preparing their remaining forces for a battle that will probably end with one of them annihilated once and for all; however, Tychoides reveals to the players that the Marauders are planning to ambush and kill the survivors, before going on to dominate the world. Surrendering access to the Technocracy's command network, he allows the players to unite both sides against their enemy, resulting in a truce that lasts for the remainder of the Ascension event.
- In Dungeons & Dragons, the Githyanki and Githzerai have been at each other's throats since overthrowing their Mind Flayer overlords due to disagreements over what they should do afterwards, with only temporary alliances of convenience to deal with any Mind Flayer threats to break up the constant infighting. However, Fifth Edition introduces the Shasal Khou, a secret society of Githyanki and Githzerai who want to end their age-old enmity.
- Oslo relates the story of the secretive negotiations between Israeli and Palestinian representatives that laid the groundwork for the 1993 signing of the Oslo Accord. In order to get the representatives to even meet face to face, a neutral third party has to intervene. Enter Norwegian diplomat Mona Juul and her husband Terje Rød-Larsen: Norway has the all-important appearance of neutrality in the Israeli-Palestinian conflict. It's much easier for Mona and Terje to get their foot in the door with both sides and get the process moving than it would be for any official operating through the American or United Nations channels.
- Step 3 of Hamilton's "Ten Duel Commandments" was to have each side's seconds attempt to negotiate a settlement acceptable to both sides, or set up a time and place for a Duel to the Death if one cannot be found. It get revisited at Step 8 when both participants are facing each other with pistols in hand, the last chance for both sides to agree to back down before the shooting starts.
- In The Longest Journey, April ends the ancient war between the Alatien and the Maerum by uncovering proof that they are actually the same species worshiping the same god.
- In Mass Effect 3, Shepard has a chance to end the war between the quarians and the geth peacefully, though there are many conditions that have to be met for this to succeed. Also, the Krogan/Salarian/Turian enmity can be mended to the point where the three races start cooperating—something deemed impossible for at least several centuries. The Turians and the Humans have the latest in species grudges, but the Turians are the most willing to help humanity out (though they have their own problems).
- And as the Extended Cut shows, the Control and Synthesis endings both result in a lasting peace between the Reapers and the galactic life, though only in the latter is it completely voluntary (in Control, Shepard becomes the new Reaper overmind and basically forces them to obey organics).
- A major plot point in Wild ARMs 5 is to reconcile the ancient conflict between the humans and the Veruni.
- In Wasteland 2, you can reconcile the warring "train tribes", the Topekans and the Atchisonians, by getting their leaders to recognize that prolonging their conflict will ultimately destroy both groups, whereas seeing past their old grudges will actually let them get the trains up and running again.
- In Fire Emblem Fates: Revelation, your goal is to end the Forever War between Hoshido and Nohr so you can fight the true enemy, Anankos.
- In Fallout: New Vegas, you can convince both the Great Khans and the Brotherhood of Steel, both longtime foes of the New California Republic, to support the latter at the Second Battle of Hoover Dam during quests.
- Devil May Cry 5: Nero, refusing to lose anyone else close to him as he did Credo, plants himself right between Dante and Vergil and demands an end to their feud. When an indignant Dante storms up to him telling him to stand down, Nero backhands him so hard he goes flying and reaffirms that he won't let the two kill each other.
- The episode "The Great Divide" of Avatar: The Last Airbender had Aang do it with two tribes of Slobs Versus Snobs by saying that he had witnessed the birth of their conflict (since he is Really 112 Years Old), which had been twisted over the century and was in fact no more than a children's game. And once the now peaceful tribes are out of earshot, he confides to Katara and Sokka that he made the whole thing up.
- Gone Horribly Wrong for the first Avatar, Avatar Wan when he separates Raava—the World-Spirit of Order—from Vaatu—the World-Spirit of Chaos—and thereby sets up the latter to plunge the world into a 10,000-year age of, you guessed it, chaos and darkness. To be fair, Vaatu abandoned his pride to take advantage of Wan's kindly nature and manipulate him whereas Raava was extremely condescending and dismissive of Wan, refusing to explain her motives for keeping Vaatu entrapped until after Wan had freed Vaatu.
- The episode "Targets" of Young Justice (2010) had Lex Luthor do it with North and South Rhelasia, which were expies of the Koreas.
- Popeye mediates the battle between Lilliput and Blefescu thusly (this after Popeye captures the Blefescu king and the Lilliputian king declares victory):
Popeye: Nobody wins! And I'm gonna steps on both of ya if ya don't shakes hands and makes peace! (They do)