The myth of the peace-loving "noble savage" is persistent and pernicious. Indeed, for the last fifty years, most popular and scholarly works have agreed that prehistoric warfare was rare, harmless, unimportant, and, like smallpox, a disease of civilized societies alone.

Lawrence Keeley's groundbreaking War Before Civilization offers a devastating rebuttal to such comfortable myths and debunks the notion that warfare was introduced to primitive societies through contact with civilization (an idea he denounces as "the pacification of the past").[1]

[1] https://www.amazon.com/War-Before-Civilization-Peaceful-Sava...

Much has been written on the topic. Here's a fairly decent book.

http://www.amazon.com/War-Before-Civilization-Peaceful-Savag...