Irredentism is a political and popular movement whose members claim (usually on behalf of their nation) and seek to occupy territory which they consider "lost" (or "unredeemed"), based on history or legend. The scope of this definition is occasionally subject to terminological disputes about underlying claims of expansionism, owing to lack of clarity on the historical bounds of putative nations or peoples.
This term also often refers to revanchism but the difference between these two terms is, according to Merriam-Webster, that the word "irredentism" means the reunion of politically or ethnically displaced territory, along with a population having the same national identity. On the other hand, "revanchism" evolved from the French word "revanche" which means revenge. In the political realm, "revanchism" refers to such a theory that intends to seek revenge for a lost territory.
Main article: Italian irredentism
The word (from Italian irredento for "unredeemed") was coined in Italy from the phrase Italia irredenta ("unredeemed Italy"). This originally referred to rule by Austria-Hungary over territories mostly or partly inhabited by ethnic Italians, such as Trentino, Trieste, Gorizia, Istria, Fiume and Dalmatia during the 19th and early 20th centuries. An area liable to be targeted by a claim is sometimes called an "irredenta".
A common way to express a claim to adjacent territories on the grounds of historical or ethnic association is by using the adjective "Greater" as a prefix to the country name. This conveys the image of national territory at its maximum conceivable extent with the country "proper" at its core. The use of "Greater" does not always equate to irredentism.
For current and historical irredentist claims, see List of irredentist claims or disputes.