Below is a section of an article called "Prehistory" from a longer WIKIPEDIA article entitled HUMAN. It's excellently written, but there is no mention of the massive, violent wars that took place during this time period and the episodes of mass slaughter that occurred. 

The article does mention Egypt (with a picture of a pyramid), and Sumerian cities in Mesopotamia. Yet not a single mention of the destruction of entire cities and slaughter of civilians that took place during this period. Why no mention of these episodes of mass-slaughter? Can anyone explain this to me?

Thanks, Richard Koenigsberg
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Until about 12,000 years ago, all humans lived as hunter-gatherers. The Neolithic Revolution (the invention of agriculture) first took place in Southwest Asia and spread through large parts of the Old World over the following millennia. It also occurred independently in Mesoamerica (about 6,000 years ago), China, Papua New Guinea, and the Sahel and West Savanna regions of Africa.

Access to food surplus led to the formation of permanent human settlements, the domestication of animals and the use of metal tools for the first time in history. Agriculture and sedentary lifestyle led to the emergence of early civilizations.

Ancient

An urban revolution took place in the 4th millennium BCE with the development of city-states, particularly Sumerian cities located in Mesopotamia. It was in these cities that the earliest known form of writing, cuneiform script, appeared around 3000 BCE. Other major civilizations to develop around this time were Ancient Egypt and the Indus Valley Civilisation. They eventually traded with each other and invented technology such as wheels, plows and sails.

Astronomy and mathematics were also developed and the Great Pyramid of Giza was built. There is evidence of a severe drought lasting about a hundred years that may have caused the decline of these civilizations, with new ones appearing in the aftermath. Babylonians came to dominate Mesopotamia while others,^[such as the Poverty Point culture, Minoans and the Shang dynasty, rose to prominence in new areas. The Late Bronze Age collapse around 1200 BCE resulted in the disappearance of a number of civilizations and the beginning of the Greek Dark Ages. During this period iron started replacing bronze, leading to the Iron Age.

In the 5th century BCE, history started being recorded as a discipline, which provided a much clearer picture of life at the time.