English Dictionary: [<Gk dispersion]
"the movement, migration, or scattering of people away from an established or ancestral homeland" or "people dispersed by whatever cause to more than one location", or "people settled far from their ancestral homelands" [Wikipedia]
Thus diaspora may describe historical mass-dispersions of people with common ethnic identities, particularly movements of an involuntary nature, e.g..
the Black Diaspora of Africans in the Americas (and beyond) via the slave trade (see also Pan-Africanism);
or more voluntary dispersions such as the Hispanic Diaspora or the Indian Diaspora (from South Asia).