It's about what happened to Russia in the year 1917 of World War 1
Answers (1)
Germany checkmates Russia can be interpreted as the tactical supremacy of German over Russia, which had lost a great deal of land over time to Germany.
The true checkmate perhaps is the loss of Russia's King (Czar) and Queen (Czarina), who had been deposed by the Bolsheviks and murdered, the first order of business for Lenin the new leader of Russia was to end the war and let Germany keep it's conquered lands in the east and save losing yet more Russian workers lives.
The postcard has all of the major players present on it;
On the left: Grand Duke Nicholas (seated), Cadorna, French and Joffre. On the right: Hindenburg (seated) and Hotzendorff.
Hope this helps!