The Soviet invasion of Poland was a military operation that started without a formal declaration of war on 17 September 1939, during the early stages of World War II, sixteen days after the beginning of the Nazi German attack on Poland. It ended in a decisive victory for the Soviet Union's Red Army. The Soviets acted on the basis of their alliance with Nazi Germany; on 1 September, the Germans invaded Poland from the west and, on 17 September, the Soviet Army invaded from the east. The Red Army quickly achieved its targets, vastly outnumbering Polish resistance, already reeling from the German blows. The Soviet government annexed half of the Polish territory now under its control and in November declared that the 13.5 million Polish citizens who lived there were now Soviet citizens. The Soviets quelled opposition by arrests, deportations and executions. (Full article...)