According to myers, in 2003 american and british leaders justified attacking iraq not as a hostile effort to kill iraqis, but as an instrumental act of liberation and of self-defense against presumed weapons of mass destruction. social psychologists would consider this an example of aggression

Instrumental or cognitive aggression: these terms are interchangeable, both meaning the aggression is planned and is used as a means to meet a goal that can't be achieved in any other way. 

Instrumental aggression is a planned attack and is typically the one means left. It is seen as necessary as no other plan has worked to achieve the goal. It is thought out and even justified by a higher moral grounds.