On 1 September 1939 Germany invaded Poland, starting World War II. On 17 September, the Soviet Union invaded Eastern Poland, and, as a result, Poland was partitioned among Germany, the Soviet Union and Lithuania. Soon after that, the Soviet Union demanded significant territorial concessions from Finland, and after Finland rejected Soviet demands, the Soviet Union attacked Finland on 30 November 1939 in what became known as the Winter War – a bitter conflict that resulted in a peace treaty on 13 March 1940, with Finland maintaining its independence but losing its eastern parts in Karelia.