Option 1 -> "unfriendly" is similar in meaning to belligerent, not opposite.
Option 2 -> "clever" relates to intelligence and is unrelated to hostility or aggression.
Option 3 -> "truculent" means aggressively defiant or eager to fight - actually a synonym of belligerent.
Option 4 -> "un-contentious" means not causing conflict or argument - the opposite of belligerent.
Hence, Option 4: un-contentious -> Belligerent means hostile and aggressive, while un-contentious means peaceful and non-confrontational, making them perfect antonyms in the context of a nation's behavior toward its neighbors -> correct