Some archaeologists have painted primitive societies as relatively peaceful, implying that war is a reprehensible modern deviation. Others have seen war as the midwife of the first states that arose as human population increased and more complex social structures emerged to coordinate activities.

A wave of new research is supporting this second view. Charles Stanish and Abigail Levine, archaeologists at the University of California, Los Angeles, have traced the rise of the pristine states that preceded the Inca empire. The first villages in the region were formed some 3,500 years ago. Over the next 1,000 years, some developed into larger regional centers, spaced about 12 to 15 miles apart. Then, starting around 500 B.C., signs of warfare emerged in the form of trophy heads and depictions of warriors, the two archaeologists report in last week’s Proceedings of the National Academy of Sciences.

One of the regional centers, Taraco, was destroyed in the first century A.D., probably by forces from Pukara, the other principal regional center of the area. Pukara enjoyed its status as a pristine state until about 500, when it was absorbed by Tiwanaku, the principal state on the other side of the Lake Titicaca basin....