There is a significant difference between an original homeland, and a promised land.
An original homeland can be left because of overcrowding, limited (&/or dwindling) resources, internal pressures, and pressure from other cultures. War, disease, colonialism, famine, opportunism, and especially overcrowding, can cause cultures to expand or leave.
Promised lands can be mythical, nearly impossible to locate or reach, over-romanticised, &/or occupied by another people.