A Fighting Chance

An 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.

The Tropes:

 * 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.
 * 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 . For the same reason Sineval was passed over for supreme command twice, as the less experienced Branmer and Shakiri are more prudent.
 * Bunny Ears Lawyer: Joe Tennant from The Dilgar War makes a spectacular return.
 * 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.
 * Continuity Nod: a few, both with the main series and The Dilgar War.
 * Did You Just Punch Out Cthulhu?: The Minbari were considered invincible in open battle until the Battle of Jericho, when Earthforce defeated and routed the Minbari in open battle.
 * 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.
 * For Want of a Nail: something went slightly different early in Earth partecipation 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 the Narn, a fleet disappeared in hyperspace from the Drazi, and the mentioned sensors from the Dilgar.
 * 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.
 * Irony: Joe Tennant first battle with the new sensors involves reproducing the Black Star ambush tactic on the Minbari using the EAS Nemesis to do the deal. After that, he has "Have introduced the Minbari society to the concept of irony" added to the ship's log.
 * 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.
 * Meaningful Name: The ship that first executes a Minbari-style jump point attack on the Minbari is called Nemesis.
 * Oh Crap: 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.
 * 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 that had broken his stealth, opened fire from long range even before realizing, just in case.
 * The Strategist: Branmer.
 * 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 Un-Reveal: in a strange way for The Dilgar War: the epilogue of that fanfiction reveals that the Drazi sent a fleet to help Earth but it disappeared in hyperspace, with the reader thinking it had been ambushed and destroyed by the Minbari. In this one 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.
 * We Have Reserves: invoked by Branmer about Earthforce, as he knows Earth can easily replace entire fleets.
 * 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.