slave labor should be added, when you conquer another country you should be able to enslave the people. Even though I don't have any countries, I think this is a good idea for those players that do.
Maybe you should be able to join other countries together to make a large one, maybe there should be more realistic war treaties from other players I know you simply conquer countries maybe you conquer half or something and enterprises should be able to sell arms to a country at war in return for money or gold coins. For example an enterprise like mine could stockpile trillions of arms and when a country goes to war the enterprise could lend it to other countries for large amounts of money.