Then it was as if waves of gasoline were poured onto the tinder. When the Hutu regime that had just carried out the genocide of Rwanda’s Tutsis was overthrown in 1994, well over a million Hutu fled into eastern Congo, then known as Zaire. These included both the génocidaires and their defeated army (the abandoned armored car in Bunia was theirs) as well as hundreds of thousands of Hutu who had not killed anyone but who feared reprisals at the hands of the Tutsis now running Rwanda.

In their militarized refugee camps, the génocidaires rearmed and began staging raids on Rwanda. To try to put a stop to this and install a friendly regime in the huge country next door, Rwanda, along with Congolese rebel allies, invaded its neighbor in 1996 in what is known as the “first war.” Mobutu’s kleptocracy in Kinshasa rapidly crumbled; the dictator fled overseas and died a few months later. Laurent Kabila, a portly veteran of some years as a rebel in the bush and many more as a shady businessman in exile, now found himself leader of a Congo where almost all public services had collapsed. He was not the man to fix them. Stearns gives a vivid anecdotal picture of Kabila as someone far out of his depth, trying to run a government by literally turning his house into the treasury, with thick wads of bills stashed in a toilet ­cubicle.

Kabila soon parted ways with his Rwandan backers. Then came the “second war”: an invasion by Rwanda and its ally Uganda in 1998. They failed to overthrow Kabila, however, because, dangling political favors and lucrative business deals, he enlisted military help from several other countries, principally Angola and Zimbabwe. A few years later he was assassinated and succeeded by his son Joseph. Eventually, a series of shaky peace deals ended much of the fighting.

But, as Stearns says, “like layers of an onion, the Congo war contains wars within wars.” For example, Uganda and Rwanda fell out badly with each other and fought on Congo soil. Each country then backed rival sets of brutal Congolese warlords who sprang up in the country’s lawless, mineral-rich east. And when Rwanda’s Hutu-Tutsi conflict spilled over the border, it fatally inflamed complex, longstanding tensions between Congolese Tutsis and other ethnic groups. This is merely the beginning of the list.

The task facing anyone who tries to tell this whole story is formidable, but Stearns by and large rises to it. He has lived in the country, and has done a raft of interviews with people who witnessed what happened before he got there. Occasionally the chain of names of people and places temporarily swamps the reader, but on the whole his picture is clear, made painfully real by a series of close-up portraits.