For two and a half weeks, the German army had been swarming over Poland. Since the start of the invasion on September 1, 1939, Poland had only offered the weakest resistance to their enemy’s armies and air force. And just when the Poles thought things couldn’t get any worse, they did.
On September 17, 1939, the Soviets attacked from the east. With well over half a million troops, the Red Army surged into Poland, in keeping with their secret agreement made with Germany back on the 23rd of August. Russian dictator Joseph Stalin called the action a “liberation”, but for thousands and thousands of Poles, it was anything but that.
Stalin had determined in his mind that all traces of Poland would cease to exist. And because he no longer viewed Poland as an entity, niceties such as the Geneva Convention and concern for the citizens had no meaning. So as the army moved westward, behind them came the NKVD with their lists of names. Polish law enforcement officers, public and government officials, professors and scientists, and military personnel were all rounded up (like those shown above). Nearly all of them would be executed.
And as with the German invasion, the Soviet invasion of Poland would be met with stern condemnation from Great Britain and France (both of whom had made military guarantees to Poland), but nothing else.
In all pratical ways, Poland was gone.