Top left: abdication of the German Emperor and proclamation of the Republic by Philipp Scheidemann, 1918

Top right: unrest on Marienplatz in Munich during the (attempted) Hitler Coup, 1923

Bottom left: destroyed synagogue in Berlin Fasanenstraße after Night of Broken Glass during November Pogroms, 1938

Bottom right: Fall of Berlin Wall, 1989

There are more events in german history connected to the 9th of November, but these four are the most important ones. The date was in discussion to become Germany's national holiday, but due to the Night of Broken Glass being too negative, the decision was made against the 9th of November and instead the 3rd of October was chosen (the date the reunification treaty was signed in 1990).