Africa's most populous nation, Nigeria has seen a rising wave of ethnic and religious bloodshed in which thousands have died since military rule ended in 1999. The introduction of strict Islamic sharia law in parts of predominantly Muslim northern Nigeria, despite opposition from non-Muslims, triggered violence in early 2001. That crisis appears to have compounded historical ethnic and regional rivalries blamed for a devastating civil war in the late 1960s in which more than a million people died.