The Belgian occupation in Germany
On November 11, 1918, at five o'clock in the morning, the German capitulation became a fact. Shortly before, the Weimar Republic had been proclaimed in Germany. The Allies occupied parts of Germany. Belgian army units also entered the Rhineland as occupiers in 1919, and later, from 1923 to 1925, a part of the Ruhr area as well.
On September 20, 1919, postage stamps were made available to the Belgian troops for the franking of mail items presented by them intended for addressees in Belgium, the Belgian Congo, and France, including the colonies. Belgian stamps were overprinted in black ink by the Stamp Printing Office in Mechelen with the names ALLEMAGNE and DUITSCHLAND. The stamps featuring the image of King Albert I and various subjects were used as base stamps.
The series was expanded with three values in 1920:
In the overprint on the stamps of King Albert I, a deviation occurs in the form of a lowercase letter E at the end of the word ALLEMAGNE.
Furthermore, there are two types of overprints for the values in Belgian francs. Type I is the edition that was first printed in 1919. Its characteristic feature is that the D of DUITSCHLAND is situated approximately below the A and G of MAGNE. The distance between the two words is two millimeters.
Type II was printed in August 1920. A distinguishing feature is that the D of DUITSCHLAND is placed exactly below the letter A of MAGNE. Furthermore, the distance between the two words is one millimeter.
From 1919 to 1930, the Rhine Province was occupied by the Allied forces. The province was divided into a Belgian, British, and French sector. From 1923 to 1925, Belgian and French troops also occupied the Ruhr area. The Belgian military used its own 'occupation stamps' in the areas controlled by Belgium. The Belgian occupation of the Rhineland ended in 1926 (Northern Rhineland) and 1929 (the Aachen region). The series of stamps was valid for postage up to and including April 30, 1931.

Beautiful series with stories surrounding the issues, with historical context.