After the defeat and partitioning of Poland by Germany and the Soviet Union in September 1939 the Soviets turned towards Finland.
They sought to push the border on the Karelian Isthmus westwards to increase the security of the Leningrad city.
After the Finns refused a Soviet offer of acquisition and exchange of land, the Soviet army launched an attack on Finland on November 30th, 1939 thus beginning the Finnish-Russian war of 1939-1940, which was also called the Winter war.
Soviet troops totaling up to one million men attacked Finland, while the Finnish forces numbered only around 300 thousand. The Finns were from the outset thus heavily outnumbered but put up a staunch and skillful defense over the next few months. In February 1940 the Soviet army broke through the Finnish defense line and streamed through inland towards the large Finnish city of Viipuri. Exhausted, the Finns made a peace agreement with the Soviet Union on March 12th, 1940, losing much of the land they sought to defend.
In the IMS archives, you can find a surprisingly large number of photos from the war. I had seen frontline photos before, but in the IMS archives, you can find many photos from behind the frontlines. I, for one, did not know about the Lotta Svärd, the Finnish voluntary force for Finnish women during the war, until I started to browse the photos from the war.