noun
allied forces; the Allies
Refers to a military coalition, often used historically for the Allies in WWII, but can apply to any allied army.
連合軍は1944年にノルマンディーに上陸した。
The Allied forces landed in Normandy in 1944.
Compound of 連合 (れんごう, 'alliance') + 軍 (ぐん, 'army').