oath; pledge; union; to ally; league, a subdivision corresponding to prefecture in Inner Mongolia

alliance; union; coalition

(of a nation) to join an alliance; (of an athlete) to join a sports team; (of an entrepreneur) to join a franchise; (of an actor) to join the cast of a movie; (of a recording artist) to sign with a label

ally

to form an alliance; to ally oneself with; allied with; aligned; to bond with

allied forces

European Union; EU

allies; united countries