German Empire
The high command under Paul von Hindenburg and Erich Ludendorff increasingly controlled the country, but in October after the failed offensive in spring 1918, the German armies were in retreat, allies Austria-Hungary and the Ottoman Empire had collapsed, and Bulgaria had surrendered. The Empire collapsed in the November 1918 Revolution with the abdications of its monarchs. This left a postwar federal republic and a devastated and unsatisfied populace, which later led to the rise of Adolf Hitler and Nazism.
Day of the founding of the German Empire
The North German Confederation had already officially adopted the name "German Reich" in its Constitution by 1 January 1871, so constitutionally speaking, 18 January was not the day of the founding. 
Celebrations were held annually on 18 January. At centralised and local events, patriotic speeches were held and songs such as "Heil dir im Siegerkranz", the unofficial anthem of the empire were sung. Celebrations also took place publicly during the Weimar Republic (1919-1933) and with the participation of high dignitaries. Nazi Germany only celebrated the founding of the German Empire in 1871.