Please help me, I don't understand
Which is true about the “push-pull” theory of voluntary migration?
The transatlantic slave trade pushed millions of Africans against their will to the European colonies.
People migrate because their personal difficulties “push” them to leave.
In the 1840s, a disease destroyed the potato crop in England, pulling people to migrate.
People migrate because a lack of religious freedom “pulls” them to a new country.