Belligerent

adjective

/bəˈlɪdʒ.ər.ənt/

Eager to fight; openly aggressive in manner.

Its opposite is not 'peaceful' but 'conciliatory'. Peaceful describes a state; belligerent describes a stance taken towards someone, so the true opposite is the stance that seeks to settle rather than the absence of conflict.

belligerent tonebelligerent nation

Same side

Pugnacious, Combative, Truculent, Bellicose

Opposite side

Conciliatory, Amicable, Pacific, Placatory

His belligerent response to a routine question turned a briefing into a confrontation.