Betrayal, dastardly betrayal!
In a move that has caught Mother Russia completely by surprise, the German army attacked across the borders, from Lithuania south to Lvov. Stavka ordered an immediate mobilization. It will take time to muster the forces and get them in place to block any German advance.
As the Germans had not yet been able to bring the French and British to their knees, and as their Italian ally is in the midst of a two-pronged attack in Algeria, as they made only slow progress in Yugoslavia, it was inconceivable to the Russian high command that the Germans would want to open up a four front war.
The situation upon mobilization:
