How did "civilization" happen (scroll down for a photo of Pharaoh Khufu's pyramid). Why did civilization come into being?

Small bands of men and women settled down in Africa for millions of years. Apart from having to defend themselves from being devoured by wild animals, homo sapiens (and related hominid species), led a relatively easy life. They didn't have to work hard to survive and had free time on their hands. In his celebrated paper, anthropologist Marshall Sahlins called hunter-gatherers the "original affluent society."

Then out of nowhere, lo and behold, perhaps 4000 years ago, homo-sapiens, the same biological creatures, suddenly began doing things differently, developing complex technologies and building monumental structures, the pyramids (see below). And began fighting monumental wars and slaughtering one another.

Still homo sapiens but creating an entirely new way of life and being. At the same time the pyramids were built, homo sapiens began fighting monumental wars. That's when our heartaches began. When "primitive" men transformed into "civilized" men. Why?

NORMAN O. BROWN: "The ambition of civilized man is revealed in the pyramid—the achievement of the first modern individualists.  In the pyramid repose both the hope of immortality and the fruit of compound interest. 

As Heichelheim showed, the Iron Age, at the end of which we live, democratized the achievements of the Bronze Age (cities, metals, money, writing) and opened up the pursuit of kings (money and immortality) to the average citizen. But the inevitable irony redresses the balance in favor of death.  Death is overcome on condition that the real actuality of life pass into these immortal and dead things; money is the man; the immortality of an estate or a corporation resides in the dead things which alone endure. 

From PBS: Pyramid: David Macaulay's 
documentary: 

The Pharaoh Khufu giving instructions to his Scribe: “You will build me the greatest pyramid of all. So that no one who sees it can doubt the power and the glory of the King of Egypt. From now until the end of time.”