BOOKS: Killing Off Innocence; Why children serve in three fourths of armed conflicts.(Children at War)

Byline: Tom Masland

Everybody recognizes the photo. The child soldier wears the uniform of an adult and carries an AK-47. His skin is smooth, his gaze steady. From Burma to Sierra Leone to Sri Lanka, he fights without remorse, capable of the most horrifying atrocities. Victim and war criminal at the same time, he and his peers have upended the rules of conflict. As Ivorian author Ahmadou Kourouma wrote in his prize-winning novel "God Isn't Under Any Obligation," "The child soldier is the most famous character of the end of the 20th century."

Why? In his landmark new book "Children at War" (269 pages. Pantheon ), P. W. Singer begins to provide some answers. A Brookings Institution political scientist who specializes in modern warfare, Singer sets out to explain why soldiers under 18 now serve in three quarters of the world's conflicts. That's a sharp break with the unwritten "law of the innocents" that has largely exempted children from conflict through the ages. A quarter century of globalization has rent traditional societies and left millions behind. As a result, the use of child soldiers has become "so common that it can be thought of as an entirely new doctrine of warfare," says Singer.

The rise in child soldiers neatly tracks the proliferation of failed states. Such states breed "coalitional aggression"--young men competing to survive, Singer observes. Add to that a glut of light, ...