What term is used for a person or nation that initiates hostilities or makes an unprovoked attack?

The appropriate term for a person or nation that initiates hostilities or makes an unprovoked attack is "aggressor." This term specifically refers to an individual, group, or country that engages in aggressive behavior or military action towards others without justification. In international relations, the aggressor is often seen as the party that starts a conflict, leading to an imbalance in peace and security.

While a defender would represent a party that protects or responds to aggression, the diplomat's role typically involves negotiation and communication rather than initiating conflict. An assailant, while it may seem similar, more commonly relates to individuals in a legal or criminal context rather than to nations or larger groups. In understanding these terms, recognizing the focus on initiating hostilities distinctly identifies the aggressor as the party responsible for starting the conflict.