The clash is between ideologies, and aggression is usually vented through the media of literature, lectures, art forms and media.
E.g. Propaganda Literature of Communism, Da Vinci Code, etc.
2. Political Motives
Aggression and persecution with political motives.
E.g. When Nero burnt Rome and blamed the Christians, executing many of their leaders.
3. Profit Motives
Aggression to eliminate economic rivalries or blockades.
E.g. Persecution of Paul by Demetrius at Ephesus (Acts 19), Persecution of Jews...