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.