You can build factories with slavery being active since last two years.Used to go to war just to "generate" slaves, but then at some point slavery prevented building factory buildings so I stopped using them for anything else except to speed up building wonders. I would really like to see an option where you could have active slavery, AND to be able to build factories etc. After playing the game "your way", as in being German Jewish Communistic Empire, which is super religious and practices active cannabilism, is "FUN".