The author of the image probably had in mind for fallen heroes the history of the Hungarian or Magyars people before the year 1000.

They were one of many nomadic tribes to come from the steppes and involved themselves in the wars that Byzantium had with who ever happened to be their northern neighbor; at the time that being Simeon I of Bulgaria. They entered the Carpathian Basin under the leadership of Árpád around the year 895 but suffered defeat against the Bulgarians. After this they moved further into the basin.

As a nomadic people they took to raiding their surrounding neighbors, one of which was the Eastern Frankish Kingdom that would become Germany. Their incursions into the west came to an end after losing to Otto I the Great at Battle of Lechfeld (955). Afterwards they would raid but only into the Balkans that would eventually end around the 970's. Grand Prince Géza became the first to convert to Christianity but how sincere he was, was suspect. His son Stephen continued the Christianisation of the Hungarians and took the title of King in the year 1000 or 1001. By this point they had left their pagan nomadic lifestyle for christian sedentary lifestyle. This being what the image seems to imply as to why they are "fallen" from their "heroic" past.

Of course this image is kinda flimsy under scrutiny if you examine what was happening in the viking realms around that time in that image. They also had begun to go through a similar process that Magyars were going through with the proliferation of Christianity. Denmark and Kievan Rus by that point was already on similar trajectory as the Magyars while Norway and Iceland would soon also reach similar stage. The Swedes were the last to Christianize among the vikings but were also the least involved in actual raiding.