There were several factors that contributed to a decrease in human population between 1000 and 2000 A.D. Some of the major factors include:
-Disease: During this period, the world experienced several pandemics and epidemics, including the Black Death, which killed an estimated 75-200 million people in Eurasia alone. These diseases had a significant impact on population size and demographics.
-War and conflict: This period was marked by frequent wars and conflicts, which caused widespread death and displacement. In many regions, these conflicts led to the collapse of civilizations and the depopulation of entire regions.
-Climate change and environmental degradation: Changes in climate patterns and environmental degradation led to crop failures and famine, which contributed to population decline.
-Migration and displacement: As populations moved and migrated, they often encountered new diseases, conflicts, and environmental challenges that further contributed to population decline.
Overall, these factors, along with others, contributed to a significant decrease in human population between 1000 and 2000 A.D. The world population did not recover until the period of the Industrial Revolution and beyond, which saw significant improvements in medicine, agriculture, and technology.