germany invades poland on september 1, 1939
france and england declare war on germany september 3, 1939

soviet union invades poland on september 17, 1939
france and england never declare war on soviet union

http://en.wikipedia.org/wiki/S...)
The Slovak invasion of Poland occurred during Nazi Germany's invasion of Poland in September 1939. The recently created Slovak Republic joined the attack, and the Slovak Field Army Bernolák contributed over 50,000 soldiers in three divisions.
http://en.wikipedia.org/wiki/C...
In 1944, the Soviet armed forces recaptured eastern Poland from the Germans. The Soviets unilaterally declared a new frontier between the Soviet Union and Poland (approximately the same as the Curzon Line). The Polish government-in-exile in London bitterly opposed this and at the Teheran and Yalta conferences between Stalin and the western Allies, the allied leaders Roosevelt and Churchill asked Stalin to reconsider, particularly over Lwów, but he refused. During the negotiations at Yalta, Stalin posed the question "Do you want me to tell the Russian people that I am less Russian than Lord Curzon?"[21] The altered Curzon Line thus became the permanent eastern border of Poland and was recognised by the western Allies in July 1945.
When the Soviet Union ceased to exist in 1991, the Curzon line became Poland's eastern border with Lithuania, Belarus and Ukraine.

http://en.wikipedia.org/wiki/M...
A deal was reached on September 29, and at about 1:30am on September 30, 1938, Adolf Hitler, Neville Chamberlain, Benito Mussolini and Édouard Daladier signed the Munich Agreement.
http://en.wikipedia.org/wiki/W...
The concept of Western betrayal refers to the view that United Kingdom and France failed to meet their legal, diplomatic, military and moral obligations with respect to Czechoslovakia during the Munich Agreement and subsequent occupation of Czechoslovakia by Nazi Germany, as well as to Poland on the eve of the World War II.
The same concept also refers to the concessions made by the United States and the United Kingdom to the USSR during the Tehran, Yalta and Potsdam conferences, to their stance during the Warsaw Uprising, and some other events.
http://www.prokarelia.net/en/?...
- Churchill and Stalin negotiated the starting of co-operation in a war of many fronts against Germany since April 1939. In July it was agreed that when Germany and the Soviet Union attack Poland, the declaration of war of the western allies would be focused only against German actions.

- On the 23rd of August 1939 Stalin and Hitler signed the so called Molotov-Ribbentrop agreement. Its secret extra protocol included the so-called concept of the sphere of interest that did not mean permission to conquer the Baltic states and Finland. It meant instead the right to demand strategic bases in case of war.

- On the 15th of October 1939 an agreement was signed between Stalin and Churchill (the allied forces). The core of it was the plan to destroy Germany both militarily and economically. Churchill’s old plan regarding the Scandinavian operation was also accepted.