Some ideas for the game
New Buildings
Hospitals
They could prevent diseases,or reduce deaths.It could costs 7000 per building?
Airports
Fast Travel troop's through provinces(only your pronvinces).10.000 per building?
Bank
You can Store money for the future,or make bigger loans.5.000 per building ?
Land Mines
Kill 15-30% of the enemy army in the built province.3.000 per mine(have a chance of 30% to kill your troops too in the province)
New Troops
Paratroopers(Planes)
he could pass through 3 provinces,and deploy 50 troops