noun
combined armies; joint forces
Refers to military forces from different units or nations operating together. Often used in historical or strategic contexts.
連合国は合同軍を編成して敵に立ち向かった。
The Allied powers formed a combined army and confronted the enemy.
連合軍 also means 'allied forces' but emphasizes the alliance itself, while 合同軍 stresses the operational combination of forces.
Compound of 合同 (ごうどう, 'combination, joint') and 軍 (ぐん, 'army, forces').