Cite the reasons the the winter war occured what was the major battle of the war

The conflict began after the Soviets sought to obtain some Finnish territory, demanding among other concessions that Finland cede substantial border territories in exchange for land elsewhere, claiming security reasons-primarily the protection of Leningrad, 32 km (20 mi) from the Finnish border. Finland refused, and the USSR invaded the country. Many sources conclude that the Soviet Union had intended to conquer all Finland, and use the establishment of the puppet Finnish Communist government and the Molotov-Ribbentrop Pact's secret protocols as evidence of this,[F 8] while other sources argue against the idea of the full Soviet conquest.[F 9] Finland repelled Soviet attacks for more than two months and inflicted substantial losses on the invaders while temperatures ranged as low as - 43 °C (-45 °F). After the Soviet military reorganised and adopted different tactics, they renewed their offensive in February and overcame Finnish defences.

the under lying reason for the winter war was soviet concern about Nazi Germany's expansionism. the secret protocol of the pact gave the soviet union a sphere of influence that included Finland, the Baltic States, and and parts of Eastern Europe. Suomussalmi is considered the the clearest most important and most significant Finnish victory in the northern half of Finland