Human beings are most unwilling to go to war. This is why events like Woolwich take place. Governments have to create the circumstances in which people are willing go to war. Otherwise they’d never do it.
Propensity to aggression is entirely environmental. Aggressive feelings do not necessarily lead to war, and can be channelled differently. Governments create an environment that makes people become more aggressive, and then they channel that aggression to the war they desire to create. Otherwise wars would never happen.