Final answer:
The phrase used to describe forced population transfer is 'ethnic cleansing', which refers to the removal of people based on ethnic or cultural differences and can include extreme persecution and violence.
Step-by-step explanation:
The phrase used to describe forced population transfer is ethnic cleansing.
This term refers to the forced removal of people from their homeland, often involving two distinct ethnic groups, with one being driven out by another more dominant group.
It can also mean cultural cleansing if the aggressor and the victim share the same ethnic background, but different cultural values, such as religion or language.
Notably, ethnic cleansing may lead to genocide, where the persecution and mistreatment can escalate to mass killings, as in the Holocaust or during the Trail of Tears. It is different from immigration or repatriation, which generally involve voluntary moves, and resettlement, which may not involve force or the specific intent to remove a particular ethnic group.