bringing together, if possible, all representatives of a particular ethnic group into one state with fixed territorial borders

Irredentism is the desire of a state or some of its people in a state for the annexation of land of another state. Those who want the land say that it really belongs to them because the other state stole it, or they wish to liberate the people who live there who have the same ethnicity or some other connection.

The term was invented in the 1870s, when the unification of Italy left out Italians who lived in Austria-Hungary.