(AP Photo)
Canadian volunteers fighting for Finland, February 24, 1940.
The German sprint across Poland in September 1939 introduced the Nazi Blitzkrieg to the world, which then watched as Hitler's forces swept over mainland Europe and bombarded Britain.
Farther north, in the frigid expanse now occupied by Finland and Russia, an equally significant battle raged in the unprecedentedly cold months of winter 1939-1940, as the outnumbered Fins took on Stalin's Soviet Union.
The two countries signed a nonaggression treaty in the early 1930s, but that did not allay Finnish concerns about their neighbor's ambitions.
Those fears were justified, as the Soviet Union surged across the Karelian Isthmus in November 1939, seeking to deepen its western frontier.
Stalin threw about a million troops into the dense forests and frozen expanses that connected the two countries, and able, determined Finnish troops turned the bucolic landscape into a charnel house for underprepared, underfed, and initially overwhelmed Soviet troops.
Finland is though to have lost about 25,000 soldiers during the 105-day conflict, while the Soviet Union was bled of nearly 200,000 troops, and hundreds more stricken by frostbite.
Helsinki eventually succumbed to the Soviet onslaught, however, signing a peace pact on Moscow's terms on March 12, 1940 - though the country did not completely capitulate and would later allow German troops to transit its territory to engage the USSR.
As the photos below show, the Finnish troops made deft and deadly use of a vicious winter and unforgiving landscape to exact the maximum toll from the Russian invaders.