"

 NPOV required  

The article seems to me to lean more towards an ""heroic"" account of the war than an encyclopedic piece seeking a NPOV.  
For instance the opening sentences of the section Soviet–Finnish relations and politics: 
""After the Soviet involvement in the Finnish Civil War in 1918, no formal peace treaty was signed. In 1918 and 1919, Finnish volunteer forces conducted two unsuccessful military incursions across the Russian border""
The Finnish doctrine is embedded in its first sentence, tying ""Soviet involvement"" in the Civil War  with the idea that it necessitated a ""peace treaty"", and then using this muddled logic as if it were an a priori justification for Finnish military incursions into Russia. (Russian involvement was perhaps half that of the German involvement and both together accounted for about 10% of the protagonists. 35% more Finns died in the Civil War than in the Winter War)
Orthodox Finnish doctrine riddles the article, even though it contains all the information needed for an NPOV.  The account of Finnish independence for instance fails to mention that the Boshevik's policy was to grant autonomy, stating the event in heroic terms instead: 
""The outbreak of the First World War and the collapse of the Russian Empire gave Finland a window of opportunity; on 6 December 1917, the Senate of Finland declared the nation's independence.""
Knowing the Boshevik's policy makes such doctrinal heroism ring hollow.
To go through the article and cite every example of the bias and absence of references would take far too long but perhaps one or two more from various angles may make the point clearer. 
The article states: 
""the Soviet Union changed its foreign policy toward Finland in the late 1930s. The Soviet Union began pursuing the reconquest of the provinces of Tsarist Russia"".
Both parts of this need substantive verifiable reference(s).  What was this change? What form did it take? In what way can it be said that the new Russia was ""pursuing reconquest""?  Is such a characterisation neutral?  The whole requires contextualisation as history is not a simple cause effect nil sum comic strip equation and there are many drivers for any situation.  In this case the pivotal role of the economic and political policies of the West towards the revolution in Russia (as previously towards the French revolution) need to be plainly set out.  However, from the implied assertions the article segues into a distortion of what would be the core issue imo for an NPOV article: 
""The Soviet leadership believed that the old empire had ideal security and territorial possessions, and wanted the newly christened city of Leningrad to enjoy a similar security."".
The ""old empire"" is implied as being the driver rather than any legitimate security concern even though these concerns are in fact detailed afterwards.  
It seems to me that the key aspect in understanding any of this is the socio-political concept of buffer states.  Again, the article contains all the information required.  It is just that it is presented in a non-NPOV form, and so ends up in the good guy/bad guy shoot out at the OK Corral story of the Finnish doctrine.  
I believe that in the West, the establishment treated Finland as a buffer state, one that stood between it and the influence of the new socialism/communism.  I believe that Finland enjoyed the consequent economic benefits that flowed from this status, and which ended recently with the end of the Cold War.  
When all these things are included and made overt, again adding nothing into the article, the following paragraphs can be seen as the key to understanding how the war broke out.
""In April 1938, an NKVD agent, Boris Yartsev contacted the Finnish foreign minister Rudolf Holsti and Prime Minister Aimo Cajander, stating that the Soviet Union did not trust Germany and that war was considered possible between the two countries. The Red Army would not wait passively behind the border but would rather ""advance to meet the enemy."" Finnish representatives assured Yartsev that Finland was committed to a policy of neutrality and that the country would resist any armed incursion. Yartsev suggested that Finland cede or lease some islands in the Gulf of Finland along the seaward approaches to Leningrad. Finland refused.   
Notwithstanding what was said at the time, history, in the simplest manner, seems to me to record its verdict on the two parties positions.  Finland's behaviour during WW2 merited her having to pay war reparations.  Russia's assessment of Finland's true position (and intent?) was vindicated.   
In my opinion the NPOV could easily be resolved by some rebalancing of the introduction and by atte