Aggression is not necessarily physical or direct. Bullying, for example, can take place not only in the playground (where it may be direct (overt) or indirect (covert, e.g., spreading rumours with an intent to negatively influence a person's social status), but also via electronic mediums, such as mobile phones and the internet.
Mummified victims of the Rwandan Genocide (1994) at Murambi Technical School. Genocide is an example of violent interpersonal aggression undertaken collectively by human ethnic and/or cultural groups in an effort to systematically kill members of other ethnic/cultural groups.
A fight is an example of interpersonal aggression. This face-to-face verbal and physical fight took place between some human beings on a street in Beijing, China, August 18, 2007, and attracted several onlookers, including a passer-by with a camera. You can see some more photos of this incident on flickr.com.
War involves persistent, intentional, collective aggression between groups, such as nations, who attempt to exert power and influence through use of military weaponry, but often also via political, economic, and social strategies.