It may start long before those who initiate a genocide or extensive mass killing come to power. As a result, the genocidal violence may seem sudden, it may seem like an eruption. But the psychological processes of individuals, the social processes of society, and the nature of the culture and changes in them have prepared this seeming eruption. Part of that ideology is the view or belief that the world would be a better place without the other group. Given such an ideology, even good things happening to the other are seen as a threat to one's own group and oneself that can give rise to violence against the other.
Bystanders have an important role in halting violence when sign of an evolution appear.
External bystanders, outside nations and the international community, have also usually remained passive. Traditionally, nations have been concerned with their own interests, usually defined in terms of power, wealth and influence. They have not considered themselves moral agents responsible for the welfare of people who are not their citizens. Frequently, nations go on with business as usual, with trade and diplomatic relations and providing aid, even after a government has begun to persecute some minority group. This was the case in Germany during the 1930s, Rwanda before the 1994 genocide and many other instances.