Why, you are totally describing Evil Genius !
http://store.steampowered.com/app/3720
There is a demo too somewhere:
http://www.gamershell.com/download_6873.shtml
I really recommend you to try the demo before buying the game, because EG suffers from very slow gameplay. It is not uncommon having to wait 15-30 minutes in realtime until all your minions have reached their destinations on the world map before they are ready to strike. Otherwise it is the most funny and most detailed game I've seen in the past 10 years.