Revanchism (from French: revanche, "revenge") is a term used since the 1870s to describe a political manifestation of the will to reverse territorial losses incurred by a country, often following a war or social movement. Revanchism draws its strength from patriotic and retributionist thought and is often motivated by economic or geo-political factors. Extreme revanchist ideologues often represent a hawkish stance, suggesting that desired objectives can be achieved through the positive outcome of another war.

Revanchism is linked with irredentism, the conception that a part of the cultural and ethnic nation remains "unredeemed" outside the borders of its appropriate nation-state. Revanchist politics often rely on the identification of a nation with a nation-state, often mobilizing deep-rooted sentiments of ethnic nationalism, claiming territories outside of the state where members of the ethnic group live, while using heavy-handed nationalism to mobilize support for these aims. Revanchist justifications are often presented as based on ancient or even autochthonous occupation of a territory since "time immemorial", an assertion that is usually inextricably involved in revanchism and irredentism, justifying them in the eyes of their proponents.