The list of units
An Army is a group of ordinary units that move and fight together. To form an army, you must build the Army unit and then 'load' other units into it. You can load up to three units, though the Pentagon increases this limit to four, if you have built it.
Building an Army
Armies can be built in cities that have the Military Academy or a Leader in them. You must have at least four cities in addition to four cities per army you have at the time that you start building an army. That is, generally you need four cities per army. But if you start building an army and subsequently lose cities to below the four city threshold, you still retain the ability to complete that army.
An army uses one, some, or all its internal units to fight a battle, depending upon the course of the fight. It functions as one unit with triple or quadruple the hit points. Therefore, an army can usually defeat any given single unit of comparable strength.
Armies are the military forces of a nation, commissioned to defend the security of their country, as well as to protect its interests across the world. Complex organizations, armies are capable of supporting extended campaigns in lands far from home. They are frequently large groups of soldiers, though armies can be comprised of diverse combat specialties. Since these organs wield considerable force, their integration and power within a nation's ruling body is heavily scrutinized.