And if you still think that people learn something - anything - from history, read this:
Note of the Soviet Government, presented to the Ambassador of Poland to the USSR B. Grzybowski
September 17, 1939
Polish-German war has revealed the internal groundlesness of the Polish state. Within ten days of military operations Poland lost all of its industrial areas and cultural centers. Warsaw doesn't exist anymore as the capital of Poland. The Polish government had collapsed and shows no signs of life. This means that the Polish state and its government effectively ceased to exist. Thus the agreements between the USSR and Poland ceased to operate. Poland, left to itself and without leadership, has become a convenient field for all kinds of contingencies and surprises that could pose a threat to the USSR. Therefore, being hitherto neutral, facing these facts, the Soviet government can no longer remain neutral.
The Soviet government also can not remain indifferent to the fact that consanguineous Ukrainians and Belorussians, living in Poland, were left to fend for themselves and are defenseless .
In view of this situation, the Soviet government instructed the High Command of the Red Army to order troops to cross the border and take under its protection the lives and property of the population of Western Ukraine and Western Belorussia.
Simultaneously, the Soviet government intends to take all measures to ensure the rescue of the Polish people, cast by their foolish leaders into an ill-fated war, and give them an opportunity of peaceful life.
Please accept, Mr. Ambassador, the assurance of absolute respect.
People's Commissar for Foreign Affairs of the USSR
Quoted from: Foreign Policy Documents, 1939, Vol 22, Book 2-M: International Relations, 1992, page 96
Hat tip: L.W.