Why are epidemics and pandemics a relatively recent phenomenon in human history?

For the greater part of man's opportunity on earth, populaces were little, scattered, and subordinate after chasing and assembling. Those infectious diseases that influenced people were either the consequence of unplanned contamination by zoonoses or lethargic contaminations that maybe had developed with people from their primate precursors. It was just because of the rural upheaval 6,000 to 8,000 years back and the resulting development of inactive populaces sufficiently substantial to help microorganisms particularly subordinate upon human has that epidemics and pandemics seem to have moved toward becoming piece of man's life (Cockburn 1963)