Your country's army will need helicopters, battle tanks, missile launchers, ships, ... only a powerful military-industrial complex can provide it with everything it needs.
Climb the ranks of your army and become a member of the country's general staff, you will then have to manage the movement of troops on the world map and their engagements in combat.
Join the army and integrate a military division, you will have to protect your country during land battles.
Join the navy and join a fleet, you will have to protect your country during sea battles.
War fleets can be used to bomb enemy coastal regions with the aim of destroying regional infrastructure and weakening the enemy.
The primary interests of war are economic and commercial, it is about keeping control over natural resources and having access to sea routes for international trade.