Medieval 2: Total War. I've been playing a recent campaign as England, and after annihilating France, Scotland and Portugal, I've ended up in the position where the Papal States hate me (and every time a Pope dies I end up being excommunicated, though I'm barely hanging onto reconciliation with the current one), and pretty much every single Catholic nation is at war with me. It probably didn't help that I managed to assassinate the first Pope after he complained about me attacking France, even though they attacked me first. My finances are a mess, and Dijon is in a perpetual state of rebellion, with me constantly having to take it back from rebels. And yet...
The last Pope decided to announce a Crusade against Rome. Yes, I hold Rome, and the Pope is currently sitting with 800 men outside Florence, while I control all of modern-day France, parts of Belgium and western Germany, and most of northern Italy (save Milan, Turin and Venice). I ended up with a meagre force of maybe 400, almost all archers and cavalry, against about four different allied armies each consisting of over 600 troops. All sitting just outside Rome, not besieging it, but just sitting there, and that was their fatal error. Using troop placement to my advantage, and getting more cavalry and spearmen to back me up after a long march from Marseille, I managed to systematically attack each enemy army in turn without them being able to use the other armies as backup, retreating back into Rome's walls whenever I finished a battle. Wave after wave of attack, and yet Rome still stood as a bastion of England's pride. I kept this up for maybe a dozen in-game years, before the Pope finally died and his successor (reluctantly) reconciled me and called off the Crusade. My finances are still meagre and I'm still at war with every Catholic nation save the Papal States, but right now my empire spans most of Western Europe, with half of Spain under my command, and is beaten in size and might only by the Mongol Hordes...
Captcha: learn the ropes. Well, it seems I've certainly done more than that... ;D