Warfare in Independent Africa by William Reno Cambridge University Press, 271 pp., $27.99 (paper)

In December 2009, the Lord’s Resistance Army, a brutal African rebel group guided by a wig-wearing commander named Joseph Kony, massacred more than three hundred people in a remote corner of northeastern Congo. Most of the victims were clubbed to death, some were killed with machetes, a few were shot, and a few more were strangled. The LRA, as it is widely known—in Congo it’s simply called tonga-tonga, which means something like “those who attack silently”—had just kidnapped hundreds of people and was moving quickly through the bush. Anyone who couldn’t keep up was killed. Most often the other conscripts, many of them children, were forced to do the killing.

Because that corner of Congo is so isolated and sparsely populated, it took weeks for news of the massacre to filter out, unusual in today’s hyperconnected world. I had to charter a plane to reach the massacre area, because there were no functioning roads close to it. I flew into a little town called Niangara, an old trading post at the confluence of two rivers. During Belgian rule, Niangara was a boom town for cotton and coffee, though you would never know that now. The roofless old Belgian houses are sinking into the elephant grass and the once-paved roads are gluey mud. There was no evidence of war or distress when I landed, not even fresh-faced foreign aid workers in their white vests. When I stepped out of the plane, onto the red dirt landing strip, all I saw were huge leafy trees, their branches dripping with mangoes, and a group of skinny men on bicycles.

This is the story of conflict in Africa these days. What we are seeing is the decline of the classic wars by freedom fighters and the proliferation of something else—something wilder, messier, more predatory, and harder to define. The style of warfare has shifted dramatically since the liberation wars of the 1960s and 1970s (Zimbabwe, Guinea-Bissau), the cold-war wars of the 1980s (Angola, Mozambique), and the large-scale killings of the 1990s (Somalia, Congo, Rwanda, Liberia). Today the continent is plagued by countless nasty little wars, which in many ways aren’t really wars at all. There are no front lines, no battlefields, no clear conflict zones, and no distinctions between combatants and civilians, which is why the kind of massacre that happened near Niangara is sadly common.

There’s often very little effort…