Which two countries contributed most to the defeat of Poland in 1939?

The two countries that contributed most to the defeat of Poland in 1939 were Germany and the Soviet Union. Germany invaded Poland from the west on September 1, 1939, employing blitzkrieg tactics that overwhelmed Polish defenses. Shortly after, on September 17, the Soviet Union invaded from the east, following the Molotov-Ribbentrop Pact, which had divided Eastern Europe between the two powers. This coordinated assault led to the swift and complete collapse of the Polish state.