A For Want of a Nail fanfiction on Babylon 5 from Lord of Misrule, the same author of The Dilgar War. The nail in question is still unknown, but the earlier effect is that Jha'dur stopped Earthforce and the League at Balos, forcing an armistice and allowing the Dilgar Imperium to survive. After the war, it continues largely as normal, until the First Contact between Earth and the Minbari. Then, as soon as they hear of it, the Dilgar do the unexpected, and offer Earth blueprints and samples of sensors that can break through the Minbari stealth, well before Earthforce can realize they need them. You can read it here.
Ace Pilot: Jeffrey Sinclair is introduced as one by virtue of being the first human to have shot down a Minbari fighter in spite of not having the sensors capable to break the Minbari stealth yet: he just took his Aurora-class Starfury against a superior Minbari fighter, managed to close the distance to thirty yards and then opened fire.
Alternate Universe: From canon B5, obviously, but it's clear that though The Dilgar War was the prequel, it wasn't the same version.
Jha'dur didn't kill the idiotic warmasters, instead handing them over to the League for war crimes trials.
The Imperium still exists in this continuity, and is headquartered one one of their conquered worlds (even though Omelos is still gone).
Admiral Hamato survived, as did several others.
Thanks to the Imperium still being a viable power, the Minbari Warrior Caste never got their hands on Jha'dur.
Attack! Attack! Attack!: standard tactic and strategy of the Windswords clan of the Minbari. That's why they lost the Black Star walking in an ambush and allowed Earthforce to throw in a black hole a Star Raiders-led fleet attacking Beta Durani. For the same reason Sineval was passed over for supreme command twice, as the less experienced Branmer and Shakiri are more prudent.
Boring, but Practical: EA tech is described as such. It's undoubtedly primitive, especially compared to some of the Minbari stuff, but it's effective.
Cool and Unusual Punishment: due Jha'dur sparing the idiotic warmasters in this continuity, they were given to the League as part of the armistice agreement to be tried as war criminal. Earth proposed Death of Personality, but the League decided to throw them in a pit filled with angry Drazi.
Talked about Michael Jankowski, who caused the war by grossly violating his orders and opening fire on the Minbari. When the Earth president discuss the matter with his staff, the punishment by law should be Death of Personality (basically a telepath would wipe out his mind and create a new one, more useful for the society), the head of intelligence suggests to just execute him as Jankowski has no personality, but in the end it's decided to extradition to Minbar, so that the Minbari can do him what they want. It's just too bad the Minbari won't communicate with Earth...
The battle of Cyrus, the first large battle between Earthforce and the Minbari, saw six hundreds Earthforce warships (including 80 dreadnoughts and 200 heavy cruisers) with relative fighters against one hundred Minbari ships with relative fighters. The Minbari were outgunned and outnumbered. Due their stealth system, better sensors and weapons with superior range, the Minbari suffered no loss and wiped out the Earthforce fleet in seven minutes, letting go one single Starfury so that he'd tell Earth the power of the Minbari.
Jericho was another curbstomp, but in reverse: Earthforce used a ludicrous amount of jamming to reduce the distance the Minbari could hit them, and, having broke their stealth, used its superior numbers, firepower, combat experience, and lots of nukes (plus the surprise that the Minbari stealth was now useless) to defeat the Minbari in open combat for the first time in one thousand years. It also helped that the Minbari fighters were all wiped out in the initial exchange (they were grossly outnumbered and had no idea that their stealth had been broken, so they were unable to escape), thus paving the way for the nuke-armed bombers and fighter runs on the cannons of the Minbari ships.
The Second Battle of Cyrus sees Shakiri's fleet annihilated.
Defeating the Undefeatable: The Minbari were considered invincible in open battle until the Battle of Jericho, when Earthforce defeated and routed the Minbari in open battle.
Do Not Go Gentle: Earth's ground-based defences against Branmer's attack include giant railguns that can kill a Minbari ship with a single hit, aerospace and atmosphere-only combat aircrafts, nuclear-tipped missiles from hidden bases and submarines, and defensive missile batteries mounted on centuries-old ocean-going warships.
Enemy Mine: The Drazi are enemies with the Dilgar due their previous genocidal rampage and the Narn due their capture of Drazi worlds during the Dilgar War, worlds they still occupy as the fanfic starts. Then someone destroyed in hyperspace a Drazi fleet sent to help Earth against the Minbari, and the Dilgar, knowing that they and the Narn could be the next on the list due being helping Earth in their own ways, are quick to inform Drazi and Narn of that and form an alliance, with the Narn even renouncing the occupied Drazi worlds for alliance's sake.
The Dilgar justified their help to Earth as part respect for Earthforce beating them due to skill and determination while the Minbari don't fight fair, and an hell of a grudge for their attempt at kidnapping Jha'dur.
Foreshadowing: After being given the job to train to combat the military personnel of the Religious and Worker castes, Branmer wonders if his recruits will be needed to defend Minbar from Earthforce and says that Earth can replace entire fleets if the need arises while the Minbari were already reducing themselves to recruit the Religious and Worker castes to back up the Warrior Caste. According to Word of God, if Earth had found a way to break the Minbari stealth they would have won by outproducing the Minbari. And that's not the fanfic's author's word of god, that's JMS' word of god.
For Want of a Nail: something went slightly different early in Earth participation of the Dilgar War, and it resulted in this continuity. It's not yet clear what, but the earliest mentioned difference it's Dal'shan surviving the attack on the Space Race.
General Ripper: Sineval is shown to be one. He never gets supreme command of the Minbari because of this.
Gondor Calls for Aid: Earth asked for help from its allies, but the League of Not-Aligned Worlds is too scared by the Minbari: the only help they get are weapons from theNarn, a fleet disappeared in hyperspace from the Drazi, and the mentioned sensors from the Dilgar.
Later chapters show that the Drazi, Dilgar, and the Narn are teaming up and are planning on involving themselves more directly.
Hoist By Their Own Petard: The Minbari tried to kidnap Jha'dur, as in canon, but unlike canon, they fail. As revenge, the Dilgar provide the Earth Alliance the ability to see through Minbari stealth... which is the greatest advantage that the Minbari have, as their tactics are inflexible, their numbers are not that large, and it takes far longer for the Minbari to build one of their ships and train a crew for it than Earth does.
Hypocrite: The Minbari Warrior Caste, as in the series, calls Sheridan dishonorable for destroying the Black Star in an ambush, without giving her a chance to defend. They're called upon it by Delenn pointing out they did the exact same thing.
Jha'dur Lampshaded it even better: to her analysis, Sheridan used exactly the same ruse the Black Star had used on his squadron, only he just needed a wrecked cruiser and some repurposed missiles in place of high technology and excessive planning, and his distress call was not fake.
Insult to Rocks: Admiral Hamato says that if Jha'dur went to hell, "Hell would be fouler for it."
Kicked Upstairs: After losing at Jericho colony, Branmer is reassigned to the 'prestigious' job of training for actual combat the military forces of the Religious and Workers castes. There's wisdom in this, as he used to be a member of the Religious Caste but passed to the Military Caste at the start of the war and knew the problems his recruits would face in becoming frontline troops, but it's clear to everyone he's just being moved out of the way for Shakiri to take over as Shay Alyt.
Know When to Fold 'Em: At Jericho Branmer orders a retreat when it's clear that Earthforce will win the battle. He then changes the order to a faster but riskier emergency jump when he sees that Earth dreadnoughts are placing themselves to use as many as possible of their ludicrously numerous guns, as remaining long enough for a normal jump would mean annihilation (and what Minbari ship were too slow or damaged to escape were in fact disintegrated).
Living Ship: Sort of. In-universe, there was a cartoon made about Earthforce ships that were alive and went around doing good deeds. Joe Tenant was pleased with the portrayal of his ship, the Nemesis, how it helped out another ship with a busted engine and helping to put it in a sling... although he does state that it would be more appropriate for the Nemesis to have been dripping with the blood of its foes, laughing hysterically the whole time.
Lock and Load Montage: the end of chapter 14 gives a glorious one, describing how earth is preparing while set to the speech the president gives for the Battle of the Line (though obviously changed for a universe where fighting back against the Minbari is an actual possibility).
Macross Missile Massacre: Some Earthforce ships have a lot of missiles, with the small Olympus-class corvettes carrying forty and the Nova-class dreadnoughts and Omega-class destroyers carrying seventy-two. And those aren't the dedicated missile ships. Those carry 120 or 160 in their racks, depending on the model, plus reloads.
Meaningful Name: The ship that first executes a Minbari-style jump point attack on the Minbari is called Nemesis.
No Kill Like Overkill: What do you call using almost all the guns of a couple hundreds Nova dreadnoughts against three or four dozens damaged Sharlins, apart from 'overkill'? It became even more overkill when Branmer cried out for emergency jump and the number of targets was reduced...
Not So Different: The Dilgar claim that this is one of the reasons why they are willing to help Earthforce. Some of them do believe it, that "At their best, we are very similar." Some members of Earthforce then try to refute it, stating that the only thing they have in common is that both races like cats.
The first large battle between Earthforce and the Minbari is an immense one for Earth, as they realize how helpless they are against the Minbari due their stealth. Then, later, the Minbari gets one in the second large battle, when their fighters are overwhelmed by the starfuries and they realize Earth has broken their stealth, and the ridicolous number of guns of Earthforce ships are aimed at their ships.
The Minbari gets another even before Earthforce can outfit its ships with the new sensors, when, during their offensive on Beta Durani, Earthforce local command killed the local hyperspace beacon network just when they were passing near a black hole. The Minbari fleet was either lost in hyperspace or entered real space too near the black hole.
Hamato and everyone else in Earthforce's chain of command get a major one when Jha'dur warn them that Branmer is coming directly for Earth using a series of temporary beacons Earthforce can't shut off.
Properly Paranoid: The main reason why Branmer is the best commander the Minbari have is that he can spot Earthforce ambushes and take precautions for the ones he can't spot: he didn't really expected Earthforce to break Minbari stealth, but he still made sure of having a retreat route available and, when assaulted from an Earthforce fleet that had broken his stealth, opened fire from long range even before realizing, just in case.
Refuge in Audacity: Branmer. Minbari pre-war military forces are depleted, Earthforce is posed to invade Minbari territory, and all she has is a collection of reactivated ships straight from the mothball yards or barely completed modern warhips manned by reactivated reservists and half-trained newbies, all from the Religious and Workers' Castes. What does he do with them to gain the two months he needs? He attacks Earth, of course.
Rock Beats Laser: Earth's tech is way behind the tech curve of the Minbari, but it is very effective anyway.
Inverted with the Minbari. The story makes a point to mention that Earthforce ships in the Dilgar War were so legendarily tough that they could limp back to drydock with over a third of their mass blasted off and not only still had survivors on board, but could be repaired and back in the fight in a few months. Minbari weapons are capable of taking out one of these ships in one shot. Just because Earth's tech is effective doesn't mean that the Minbari tech isn't.
This trope, while impressive for Earth Force, is also one of its key weaknesses. Because they are so primitive, their ships burn through fuel and supplies much faster than other races, a weakness that makes it hard for the Alliance's ships to go on extended campaigns without long supply lines... which Branmer takes advantage of by attacking Earth.
Sci-Fi Writers Have No Sense of Scale: Mostly averted. Justified in the case of one Starfury having to close to thirty meters to destroy a Minbari Nial, but that was how close the fighter had to physically be in order to not only break infamously tough Minbari stealth systems but to accurately target it.
Earthforce has admiral Akira Hamato, who this time survived the Dilgar War but resigned in protest for the armistice (he knew the Dilgar couldn't replace the horrifical losses they had taken stopping him at Balos, and would have falled to another attack, but the governement didn't want to lose the troops stuck on Balos). He rejoined the fleet after Jericho to help train the reserves and be the public face of Earthforce.
Temporal Paradox: Averted: in this story, Babylon 4 arriving in the past is a fixed event, and what happened after that an alternate universe. Meaning that if the Minbari exterminate Mankind they won't lose the Great War against the Shadows in their past.
Time Travel: The Dilgar discovers it happened when they find Babylon 4 as Valen's battlestation in the Minbari records.
The Unreveal: in a strange way for Babylon 5: the RPG says the Drazi had sent a fleet to help Earth at the start of the Earth-Minbari War only for said fleet to disappear in hyperspace, with the implication being it had been ambushed and destroyed by the Minbari. In this story we see the counterpart of that scene... And discover that the Minbari tried but arrived late, and there's no hint at who did it.
The Dilgar speculate that it has to have either been a First One (such as the Vorlons) or some unknown power that wants the Minbari to win the war. The truth is unknown. Interestingly, if the goal was to help the Minbari win the war, it backfires spectacularly, as it serves as one of the motivations that makes the Dilgar, Drazi, and Narn band together to help save the earth.
We Have Reserves: invoked by Branmer about Earthforce, as he knows Earth can easily replace entire fleets.
Heavily averted with the Minbari. Their main strength is that a) they're more technologically advanced than pretty much everyone else in known space (save the First Ones, like the Walkers, the Shadows, or the Vorlons), and b) that their stealth tech is nearly unbeatable, meaning that even if the enemy is capable of fighting their aforementioned supertech, they likely won't be able to hit them. Coupled with a relatively peaceful past and fearsome reputation, they don't have nearly the amount of ships that a protracted campaign requires, and by chapter 14 they're nearly out of combat vessels after the multiple, devastating victories that Earth has scored against them.
Worthy Opponent: The Dilgar justified their help to Earth because they were, while the Minbari were not. Then we have a meeting between warleader Stro'kath of the Drazi and Supreme Warmaster Dar'sen, direct opponents during the Dilgar War, and the first thing they say each other is that they were just that, and that one day they'll duel to see who's the best combatant, because as generals they were equals.
In chapter 13, Jha'dur declares that Hamato was hers, and that only Dar'sen and Branmer could join their 'club'.