Growing your army is central to success on the global stage, and so it is imperative that your nation is equipped to recruit, supply and support your forces.
Building Recruitment Offices in your territory will automatically recruit and train your citizens into infantrymen, who will form the bulk of your military.
Naturally, you cannot win a war on numbers alone, and so you can diversify your forces by building advanced structures such as barracks, workshops and factories, harbours and aerodromes. These structures will unlock more dangerous land units, such as cavalry or tanks, as well as aircraft and warships.
Remember - the more flexible and diverse your army, the more strategic options are open to you.