I feel like the combat system is way too basic. If a few things were added, adjusted and tweaked I feel like it would be better.
TRAINING-
When troops are being manufactured/deployed, they need to be trained. The amount of training will impact their chances in combat. If training is longer, it will take longer for troops to be deployed, but they will be stronger and take less casualties. Less training will take troops less longer to be deployed but they will be weaker and take more casualties.
EQUIPMENT-
Adequate equipment and weapons are the backbone of any military. You can change the weapons or equipment that troops use. Higher standard weaponry and equipment will make troops stronger, but will make troops more expensive to deploy and maintain.Lower standard weapons will make your troops weaker but will make troops less expensive to deploy and maintain. This also applies for aircraft and vehicles, just with different generations of vehicles or aircraft.