First, this is not how the game was intended to be played. However, the latest patch has led to some unintended functionality and it's fun to exploit!
Here's how to simulate a Zombie Apocalypse in Fallen Enchantress and always win in 10 easy steps.
1. Create a custom kingdom/empire with endless legion, civics and builders. Weakness: fire, I mean, vulnerable. Name it Zombies.
2. For extra effect, choose a strength heavy race like trogs.
3. Your sovereign is mostly up to your choice, though I'd recommend 2 points in air and 2 points in fire. Nothing's worse than fast zombies with tireless march. Warlord, tactician, brilliant, discipline with an axe for more cheese. Name it Zombie King.
4. Start the game, and go for a decent size map to really spread your undead curse. I'd recommend medium. Difficulty doesn't matter too much. "Hard" just means that the enemy sovereign takes a while to hunt down, but zombies always win in the end.
5. Any starting location is fine, but it's nice to have 3 or 4 materials for when you aren't spewing zombies. Control + N to recreate the map if you are picky.
6. Found a kingdom and go to the design menu.
7. Click on pioneer then edit. Clubs, conscripted, weak and scout. Call it walker. These cost 1 production, have 0 gildar maintenance, can settle, can create outposts, feel no pain, do not require food, and can even take down ogres in large enough groups.
8. Hide all other designs, you won't need them.
9. Queue up dozens of walkers and rush each turn for 1 gildar. Make sure the queue is always sufficiently full. Every city should follow this pattern.
10. Trading is the most important first tech for roads, followed by training, logistics, and drills. Spread out with as many cities as possible, always colonizing the nearest available spot since grain and materials really don't matter.
*Sell most items for gold and rush out some inns if you feel like it for faster research.
*Mana isn't required but can add to the fun.
*Create stacks led by heroes, and create stacks without. Send in the stacks without a hero and hit auto-resolve to weaken up anything that's too powerful.
*Avoid life leech enemies like the assassin demons. They eat walkers.
*Talk to the richest non-zombie. Say that you will go to war with one of their enemies, and ask for gold and other goodies in return. You were going to eat them anyway, so why not get a stupid human to pay you to do it?
*Set taxes to 0% and don't build buildings with maintenance except + to research.