irredentist

irredentist \ir-i-DEN-tist\, noun:

1. a member of a party in any country advocating the acquisition of some region included in another country by reason of cultural, historical, ethnic, racial, or other ties.
2. (usually initial capital letter) a member of an Italian association that became prominent in 1878, advocating the redemption, or the incorporation into Italy, of certain neighboring regions (Italia irredenta) having a primarily Italian population.

adjective:
1. pertaining to or supporting such a party or its doctrine.

Although the U.I.C. had popular support, its senior members included irredentists and Al Qaeda veterans, worrying Somalia's neighbors.
-- Xan Rice, "Now Serving," The New Yorker, Sept. 30, 2013

In Evelyn's face, I saw the travels of Marco Polo, the fall of Constantinople, the irredentist yearnings of Hungaro—Romanians.
-- Leonard Michaels, The Collected Stories, 2007

Irredentist entered English in the late 1800s from the Italian word irredent which literally meant "unredeemed" but more importantly referred to an adherent of a specific political party.