Rhine crisis

Borders of the German Confederation, c. 1840
The Rhine as France's eastern border, 1806

The Rhine crisis of 1840 was a diplomatic crisis between the Kingdom of France and the German Confederation, caused by the demand by French minister Adolphe Thiers that the river Rhine be reinstated as France's border in the east, at a loss of some 32,000 km2 (12,000 sq mi) of German territory.

The territories of the Left Bank of the Rhine, which French troops had conquered in 1795 and formally annexed in 1797, had been returned to German (mostly Prussian) control after the 1815 Congress of Vienna, forming the Rhine Province. After a diplomatic defeat in the Oriental Crisis of 1840 France shifted its focus to the Rhine, and the French government, led by Adolphe Thiers, restated its claim to areas on the left bank, to re-establish the Rhine as a natural border between France and Germany. These claims stoked resentment among the Germans against the French, and increased nationalism on both sides. New nationalist songs were written in France and Germany and achieved huge popularity, most famously the German songs "Die Wacht am Rhein", "Der Deutsche Rhein" and the "Lied der Deutschen" (the national anthem of Germany since 1922). In the end, the crisis passed peacefully, when Thiers resigned as prime minister and a more conciliatory government was installed in France.