To level-up your Troops you will need Argon and time. With every next level it will become expensive in Argon and more time-consuming. There is a limit for the number of units you can have. To increase this limit, you'll have to build camps. More camps will need your headquarters (main building) to be upgraded too, as well as require resources and time (interdependent economy of the game). During a battle, all troops used will be spent: you will lose the troops used even if you win the battle. Therefore, demand for Argon of the entire game will increase.
If you want to produce new types of troops, build barracks and camps to increase the number of units in the raid.