That's impressive video Human Population Through Time which you will see below, describes the growth of the earth's population over the last thousand years. You will notice that it took a long time to populate explosion.
To be more specific it took us 200 thousand years to reach the first billion people, but only 200 years to hit the seven billion mark. 
Watch the video with the map that tracks world population growth. The video shows how we spread around the world and highlights the empires and historical events during duration of years.
The very interesting Human Population Through Time video to watch was uploaded to YouTube by the American Museum of Natural History or the American Museum of Natural History.
Watch it
