Airlift cards with troop limit
Airlift cards with unlimited amount of troops are unrealistic for diplomacy roleplay gameplay and benefit more the stronger players. Games with no airlifts allows for a different gameplay e.g. you can easily declare war on more powerful countries with colonies and just take the colonies without them being overwhelmed by the entirety of their force or it makes it easier to declare on someone who's not expecting it, so you need to manage your borders better. It can however feel a bit limiting to have no airlifts. Airlifts with troop limits would allow for a compromise between the 2 gameplays.
Surely it can be also applied similarly to allow different strategies in non-diplomacy games.