Welp, that all sounded a lot more exciting to read about than it was to live through. I thought I had put together a respectable military and economy for this point in the game, with reinforcements getting pumped out at a fair clip, and three multi-stack armies full of tier 2-3 troops. I was sadly mistaken.
I sent them in different directions, hoping to find a weak point in @Valambrian’s defenses, but everywhere they arrived, he had overwhelming force available.
One was crushed in the first attack of the war. I had seen an army that looked roughly equal to mine in his frontier city, and thought I could circle around to either find a softer target or lure his army to fight in an open field. But it turned out he had an entire extra stack full of tier 3s hiding out of sight, and was able to wipe out my army without significant losses.
The second traveled through the underground to pop up in what I hoped was a less-protected backwater. They managed to give him a bloody nose, taking one city and a decent stack of defenders, but took heavy losses in the process, and were immediately destroyed the following turn.
The third headed east trying to hit some of his underground holdings. They encountered an army that they might be able to beat in a fair fight, but it was parked in a chokepoint such that only one of my stacks could fight at a time against three of his. They withdrew to try and rush back to defend, but it was far too late.
By this time, his army that had kicked off the war had conquered my few surface holdings and was rampaging around in my homeland and wiping out my reinforcements before I could gather them all together. My assassins managed a couple pinpricks, but everything I had left in the area was severely outclassed. I threw my remaining reserves into a last-ditch effort to retake my throne city while there was only one enemy stack in position to defend it, but it wasn’t close to enough. With that gambit failed, and my last intact military force 6+ turns march away from being able to help, I threw in the towel.
Hats off to @Valambrian for clearly being on another level in mastery of this game’s mechanics. I felt like my empire was developing pretty well, but by the time he declared war on me he had about 2.5X my military score, and was pretty close to equaling the rest of us put together.
In retrospect, I should have expected this sort of bloodbath after seeing him get the achievements for 100 units when I had 52, a level 15 hero when my best was 8, a tier 4 unit before I had tier 3, and researching every skill (!) when I was still 30+ turns away.
Good game all, and congrats to @Valambrian.