Why did hitler allow soviet troops to occupy eastern poland after he took control of the land?

On this day in 1939, Soviet Foreign Minister Vyacheslav Molotov declares that the Polish government has ceased to exist, as the U.S.S.R. exercises the “fine print” of the Hitler-Stalin Non-aggression pact—the invasion and occupation of eastern Poland.

Explanation:

Hitler’s troops were already wreaking havoc in Poland, having invaded on the first of the month. The Polish army began retreating and regrouping east, near Lvov, in eastern Galicia, attempting to escape relentless German land and air offensives. But Polish troops had jumped from the frying pan into the fire—as Soviet troops began occupying eastern Poland. The Ribbentrop-Molotov Non-aggression Pact, signed in August, had eliminated any hope Poland had of a Russian ally in a war against Germany. Little did Poles know that a secret clause of that pact, the details of which would not become public until 1990, gave the U.S.S.R. the right to mark off for itself a chunk of Poland’s eastern region. The “reason” given was that Russia had to come to the aid of its “blood brothers,” the Ukrainians and Byelorussians, who were trapped in territory that had been illegally annexed by Poland. Now Poland was squeezed from West and East—trapped between two behemoths. Its forces overwhelmed by the mechanized modern German army, Poland had nothing left with which to fight the Soviets.

As Soviet troops broke into Poland, they unexpectedly met up with German troops who had fought their way that far east in a little more than two weeks. The Germans receded when confronted by the Soviets, handing over their Polish prisoners of war. Thousands of Polish troops were taken into captivity; some Poles simply surrendered to the Soviets to avoid being captured by the Germans.