noun
depopulation
dee-pop-yuh-LAY-shuhn/ˌdiːˌpɑːpjuˈleɪʃn/
A reduction in the number of inhabitants of a place.
Rural depopulation leaves many small towns with empty homes and schools.

Etymology
Latin depopulatio meant 'laying waste' or 'pillaging.' Early English may also have referred to destroying or expelling inhabitants, connecting that devastation with the modern sense of a sharp loss of residents.
In context
we left here in our Millions some never to return there was a huge depopulation of this country
More examples
- The factory closure accelerated the town's depopulation.
- Affordable housing could help slow depopulation in the region.
- War and disease caused widespread depopulation.
Forms
depopulation
depopulate verb — Reduce or remove a place's inhabitants.