First the good news: LeBlanc's main message is right. People in almost all societies have fought, and very often it's all about resources. Traditional societies of all sorts, from hunter-gatherers to early states, often overused their environments badly, and then either tried to cope by taking resources from the neighbors, or weakened themselves to the point where the neighbors could scarf up on them. LeBlanc urges us contemporary humans to take heed, and clean up our ecological act so that we can reduce (hopefully eliminate) the danger of war.
So far, so good. Thus, on balance, this is a good book and a very valuable one. LeBlanc notes that whatever innate aggressions humans have, their actual wars are typically over land and resources, and thus are preventable. We all need to hear this, in an age when politicians and writers love to naturalize war and aggression as inevitable. (Yes, I know, war isn't just about resources, but it usually involves much concern about them.)
The problems come with LeBlanc's exaggeration and sometimes shaky scholarship (on which see exchange of letters in ARCHAEOLOGY for Sept.-Oct 2003). First, while the myth of the ecologically harmonious "savage" was once common and is still with us, the myth of the peaceful savage seems quite rare. LeBlanc cites only one source for it, and he's wrong about that one. He cites Rousseau (hardly an anthropologist). In fact Rousseau never used the term "noble savage" (it's from Dryden), and R's "savage" was the chimpanzee, of whose sometimes-violent behavior R was well aware. (He tells some stories of their attacks on Africans.) Anthropologists know traditional people are often warlike. H. H. Turney-High's foundational review PRIMITIVE WAR (oddly, not cited by LeBlanc) established a baseline on that, many decades ago. Lloyd Warner (whom LeBlanc does cite) noted that Australian Aboriginals waged war about as often as Europeans, with casualty rates (and rhetoric!) comparable to WWI. Raymond Kelly and Brian Ferguson claim no "warfare" for simpler societies (in recent books) but it's a definitional difference; they define warfare as formal, huge-scale, organized conflict, and don't count the small but bloody feuds and battles almost universal among traditional peoples. I really don't know of anyone who thinks simpler societies were peaceful, but my panel of popular-culture experts (a.k.a. my family) assure me that the New Age and Goddess-worshiping set does indeed so believe. (I assume that Diana Muir's comments on anthropologists, in another Amazon review, refer to textbook accounts of ecological harmony; they certainly don't apply to the anthro literature on war.)
On ecology, while LeBlanc is right that lots of people mess their environments up, he exaggerates it, and uses a ridiculously strict definition of "conservation" that makes it virtually synonymous with "preservation." This would rule out modern soil conservation, water conservation, duck conservation, game animal conservation, etc. Traditional people everywhere figure out how to manage their environments well enough to let them survive; they sometimes overuse resources, and even ruin whole ecosystems, but usually they do well enough--though not well enough to prevent occasional war.
All this would be trivial if it weren't for the very strong possibility that LeBlanc's book will be misunderstood, by superficial readers, as a claim that "savages" are the treacherous, destructive bloodthirsty, violent, cruel, endlessly-warring beasts that they were said to be in all the earlier literature--from Thomas Hobbes to Hollywood cowboys-and-Indians movies. (Hollywood's recent glorification of the Indian is small recompense for nearly 100 years of portraying Indians as mindless butchers of cowboys and settlers.) In my experience, for every person who believes in the peaceful, harmonious savage, there are hundreds who believe in the Hobbesian one. These people usually follow Hobbes in assuming that we civilized folk have nothing to learn from "savages" except that we need a powerful king or dictator to keep us in line. If I read LeBlanc aright, this is NOT what he is saying, and readers should be warned not to make too much of his lurid title and occasionally (though not usually) exaggerated claims.