It's inspired by this - TankLarp
If you watch the video, you'll see that TankLarp is a curious mash-up of medieval and modern. And they do have armored vehicles (armored personnel carriers actually). We wouldn't do that.
My friend's initial idea was a LARP using World War I level technology. That has us off and running. Here is a quick backstory I ginned up.
Many years ago, the inhabitants of the northern continent of the planet developed advanced machine age technology. However, two great alliances formed – the free states and the evil empire. War broke out. In the bitter conflict, the evil empire was defeated, but the entire continent was devastated.
The few survivors took the remnants of their technology, fled to, and settled the southern continent. There, they encountered an array of cultures, predominantly of a medieval technological stage of development. With limited access to materials necessary for machines, a hybrid society developed where modern firearms supported rather than supplanted old-fashioned hand-to-hand combat.
But as this new society stabilized, a new threat emerged. A reborn evil empire has arisen in the east and is slowly conquering its neighbors. The evil empire has sent agents into its opponents’ nations to foster discontent, stir up conflict between nations, and foment armed insurrection.This gives us an excuse to mix medieval and firearms. I'm now on a steampunk / dieselpunk kick. I added firearms (i.e. Nerf blasters) to the combat rules and am researching garb. I think early 20th century (especially Boer War and Boxer Rebellion) uniforms would work well for muggy Florida. Stay tuned for more developments.