Revanchism, from French revanche or revenge, is a term used since the 1870s to describe the desire to reverse territorial losses by a country after losing a war. Revanchist politics rely on the identification of a nation, of a people, with a nation-state. This mobilizes ethnic nationalism, claiming territories outside of the state where members of the ethnic group live.
See the strong desire during the French Third Republic to regain Alsace-Lorraine from Germany after defeat in the Franco-Prussian War of 1870-71. French Emperor Napoleon III had declared and lost the war. In the Treaty of Frankfurt, France lost Alsace-Lorraine, which France under King Louis XIV had previously annexed from Germany in the 17th century.
French revanchism was one of the forces behind the Treaty of Versailles, which ended World War I. Alsace-Lorraine went back to France. Blame for the outbreak of the the Great War was pinned solely on Germany. Huge reparations were extracted from the Germans.
The United States Congress rejected the Versailles Treaty, citing its harsh, unfair and one-sided punishment of Germany, and warning against the inevitable development of German revanchism.
Alsace-Lorraine. Just one piece of territory in dispute between two neighbors. One of many examples in European history. Their experience as a people, their historical consciousness, has taught the Germans to seek lasting resolutions to conflicts. Acceptance, freely chosen, is the foundation.