November 1918 insurgency in Alsace–Lorraine
As a result of the end of World War I and the German revolution of 1918–1919, an insurrectionary movement inspired by communism formed workers' and soldiers' councils in several cities of Alsace–Lorraine from November 8 to November 22, 1918. The red flag was thus hoisted atop Strasbourg Cathedral.
Source: Wikipedia — November 1918 insurgency in Alsace–Lorraine (CC BY-SA 4.0)