I can't advise on the audio problem, sorry. However, it seems now they don't populate nearly fast enough. I used no weapons until about 200 years and the pop was still under 50. I'm sure it'd hit 3000 by then before.

Buttons working now (as I guess you know). Nuke-spamming causes everything to die and keeps the pop at 5, not 0? The sounds for the other two are a bit annoying, maybe have text saying "Riot starting" and ending, and the same for plague, so it's clear when they end? Still, I like it :)

Please note : I've fixed the slow execution problem. I'm pretty sure it was to do with the GreenfootImage class (initialising it a million billion times is silly).

I don't see any buttons, and it didn't stop at 3000. I think the speed of the game is fine though, assuming the buttons just require 2 clicks to wipe people out :)