What role did a changing environment play in the way peoples and civilizations changed?

a. environmental changes forced people to migrate to other areas.
b. environmental changes forced people to form armies to conquer other territories.
c. environmental changes often aided in the establishment of new farms.
d. environmental changes forced people to move into cities.

In my view, environmental changes often lead to global migration, because people need particular conditions to live. So the most suitable option is: A. Environmental changes forced people to migrate to other areas. The number of environment migrants still grows and by 2050, in about 200 million people will leave their homes because of environmental changes.

How life was like during the Great Depression.