From the very beginning it was obvious to all that there was no legal basis for Russia to invade Finland. Nikita Krushchev, Russian leader in the 1950s, wrote that “There's some question whether we had any legal or moral right for our actions against Finland. Of course, we didn't have any legal right. As far as morality is concerned, our desire to protect ourselves was ample justification in our own eyes.” [p. 17] Finland had only become an independent nation in 1918, and even then quickly devolved into a civil war that lasted several months. This meant that the fledgling Finnish army was slow to develop. By 1939 there was not much of an army, navy, nor air force. It would be difficult for Finland to find outside help as well, since World War II had just begun, and other potential allies had military and political quagmires of their own.
Russia is in Groundhog Day mode, repeating many of their same mistakes and assumptions from the Winter War against Finland in 1939. There are many eerie similarities, but suffice it to say that Russia is still willing to upset the world and kill their own for goofy reasons.