supporting or relating to a policy of returning land to a country that it belonged to in the past

They asserted an irredentist claim on the territory. 他们对这块领土断然提出收复要求。

nationalist and irredentist forces 民族主义和领土收复主义势力

someone who supports a policy of returning land to a country that it belonged to in the past

The people threw out the irredentist and elected a peacemaker. 人民将领土收复主义者赶下台，选举了一名和平人士。