The self-declared Islamic State, its predecessors and allies have killed more than 33,000 people since 2002, researchers at the University of Maryland say in a report to be released Tuesday.

The report covers not just the core Islamic State group, which is involved in a bitter war with government forces and others in Iraq and Syria, but also earlier groups that eventually morphed into the Islamic State and terrorist organizations that have pledged allegiance to it.

In all, some 30 organizations across Africa and Asia have thrown in their lot with the Islamic State, the University of Maryland researchers found, spreading violence from Nigeria to Bangladesh. […]