What Triggers Religious Violence?

 The methodology is somewhat dubious so take it for what it is worth.

The findings revealed that the most common conditions that enable long periods of mutually escalating xenophobic tension occur when social hazards, such as outgroup members who deny the group's core beliefs or sacred values, overwhelm people to the point that they can no longer deal with them. It is only when people's core belief systems are challenged, or they feel that their commitment to their own beliefs is questioned, that anxiety and agitations occur. However, this anxiety only led to violence in 20% of the scenarios created -- all of which were triggered by people from either outside of the group, or within, going against the group's core beliefs and identity.

From here.