### New Features
- **Advanced Mine & Super Mine**: Mines automatically upgrade after 10 and 20 turns, generating up to 75 and 100 gold per turn!
- **Super War Factory, Super Airport & Super Dock**: These production buildings automatically upgrade after 20 turns, gaining 2x build speed and can even produce 2 units in one turn!
### Improvements
- **AI Balance**: Different AI difficulties now have appropriate production building limits
- **State Preservation**: Unit upgrades/transformations retain HP, experience, level, and other states