The army is built from two pools: SOLDIERS (troops) and OFFICERS. A Military School trains soldiers and a War Academy trains officers, up to the limit you set. You can also discharge them.
Each piece of equipment needs SOLDIERS and OFFICERS per lot, and OFFICERS can be the bottleneck (aircraft need many). AUTONOMOUS equipment (droids, autonomous tanks, spaceships) needs NO soldiers or officers but consumes chips, AI chips or nuclear batteries.
CONSCRIPTION: an effective mass army with plenty of cheap soldiers and basic equipment (rifles). Without it you have a professional (expensive) army. Equipment costs maintenance, fuel and wages.
Weapons technology unlocks through research: tanks and aircraft → lasers, the navy (ships and submarines), war robots, autonomous aircraft, droids and the SPACE WARSHIP.