The 3rd millennium BC spans the Early to Middle Bronze Age. It represents a period of time in which imperialism, or the desire to conquer, grew to prominence, in the city states of the Middle East, but also throughout Eurasia, with Indo-European expansion to Anatolia, Europe and Central Asia. The civilization of Ancient Egypt rises to a peak with the Old Kingdom. World population is estimated to have doubled in the course of the millennium, to some 30 million people.