A more thorough explanation:

Belligerent (noun) refers to a country that is involved in a war or other armed international conflict. It is the opposite of neutral.

Belligerent (adjective) describes a person or group that is hostile, aggressive, or ready to fight.

Noun: During World War II, Germany was a belligerent country.

Adjective: The belligerent attitude of the opposing team made the game very intense.

In the first example, Germany was actively involved in the war, making it a belligerent country. In the second example, the opposing team's aggressive and hostile behavior created a belligerent atmosphere during the game.