Usage patterns
〈国〉が軍隊を持つa country has (maintains) armed forces
That country has a strong military.
軍隊に入るto join the military
He joined the military at age 18.
軍隊を派遣するto send (deploy) troops
The government deployed troops to the border.
軍隊を率いるto command (lead) the troops
The general led the troops into battle.