Wartime propaganda material, whether in terms of badges or postcards, is an almost inexhaustibly rich collection area. Throughout the Great War, German friendship was of particular importance. Not only because Germany was already an allied power before the war, in contrast to Turkey and Bulgaria, which only became allies after the outbreak of the war.
Language identity and kinship ties between the ruling families also played an important role in this. Of course, the kinship did not prevent the British and Russian rulers from going to war with their cousin… But still, the Habsburg family was connected to the German ruler and the German aristocracy by many ties of kinship. The war fought by Austria and Prussia for the unification of Germany was already fading of the 50 years that have passed, although Franz Joseph, who reigned for an extremely long time, surely remembered the experience of failure. Of course, the memory of the decisive battle in Temesvár in 1849 against the Hungarian revolutionary army, which confirmed him on the throne, must have made him more happy, since he hung the painted battle scene over his bed.
This post shows a very nicely detailed couple portrait badge with the swords symbolizing friendship of the two armies. The exaggeratedly pathetic representation of the correspondence card used as a background seems a bit grotesque to me. People did not deify the two rulers in this extreme way.