act of aggression
Refers to a concrete action that constitutes an invasion or aggressive military act, often used in political or legal contexts.
That military action is clearly an act of aggression.
侵略 is the broader concept of invasion or aggression, while 侵略行為 specifies a concrete act or instance of aggression.
Compound of 侵略 (invasion, aggression) and 行為 (act, deed).