This is about the Winter War and Continuation War. They were part of WW2. To understand them a bit of history is needed. Finland was part of the Russian Empire when the October Revolution happened. After the Revolution, Lenin proclaimed that all the constituent nations of the Russian Empire were now free to choose their own path. So Finland (and many other nations like the Baltics, Georgia, etc) declared independence. The Finnish Civil War broke out, between the finnish whites (monarchists/fascists/anticommunists), mainly composed of petty and big bourgeoisie who wanted to be completely independent from the USSR, be capitalist and ally with the German Empire (which at the time was still at war with the USSR since WW1 was still going on) and the finnish communists, mainly workers and peasants who were supporters of Lenin, had proclaimed the Finnish Socialist Workers Republic and wanted to join the USSR. While Lenins bolsheviks did help the finnish communists, the german advance was too much. Lenin had to sign the humiliating Treaty of Brest Litovsk, a peace treaty between the USSR and the Central Powers (Germany, Austria-Hungary and the Ottoman Empire). The treaty ceded Finland, Lithuania, Latvia, Estonia, Ukraine and Belarus to the German Empire and Georgia, Armenia and Azerbaijan to the Ottoman Empire. Thus, Lenin had to withdraw troops from Finland and stop helping the finnish communists. While they continued fighting, it was a lost cause and the german troops crushed them.

With the collapse of the German Empire at the end of WW1, german troops withdrew from Finland and Finland became completely independent. The new finnish state, far from the “wholesome liberal democracy” mainstream academia paints it as, was a right wing authoritarian regime. Communism was banned, and most of the finnish communists who had lost the Civil War were either massacred together with their whole families or imprisoned for a very long time. Massacres against communists were very common in the years after the war. As the 1930s arrived, Finland became more and more fascist and anticommunist. This placed them for a possible alliance with Nazi Germany against the hated communist USSR. The finnish bourgeoisie was more than happy to ally with nazism to destroy socialism. And so they did.

Now Leningrad (now Saint Petersburg), the most important city in the USSR after Moscow, was (and is still nowadays, which makes Finland joining NATO very dangerous) very close to the border with Finland, making an attack on Leningrad from Finland very easy. For this reason, in 1939, seeing the soviets the antisoviet alliance forming between Finland and Nazi Germany, they had to secure their borders. They invaded and liberated the Baltic States (who were also fascist anticommunist dictatorships allied with the nazis) and they tried to negotiate with Finland. They offered to exchange territory. Finland would give the USSR their territories surrounding Leningrad and the USSR would give Finland a territory of their choice. Finland refused. USSR even offered to just lease them or even buy the finnish territories but Finland refused to negotiate. Seeing the finnish nazi alliance was a done deal, the USSR in 1939 invaded Finland to protect itself. This was the Winter War. The plan was to invade and bring the finnish communists to power, as had been done in the Baltic States where it worked perfectly since communism was very popular there despite being brutally supressed. The finnish communists proclaimed the Finnish Democratic Republic, a socialist republic, in the areas liberated by the USSR.

Unfortunately, the plan didnt work, since finnish communism had been completely destroyed by the finnish fascists. While the USSR did manage to secure Leningrad, they failed to topple the finnish fascist regime. The small Finnish Democratic Republic joined the USSR as the Karelio-Finnish Soviet Socialist Republic (it later joined the Russian Soviet Republic where it remains today). In 1940 a peace treaty was signed and the Winter War ended. But Finland was still fascist and a nazi ally. So when Hitler launched Operation Barbarossa (the nazi invasion of the USSR) in 1941, Finland joined in in the invasion, seeking revenge against the communists. This was the Continuation War. In the end, Finland, along with its nazi allies, lost WW2. The finnish fascists were put on trial for war crimes and imprisoned. Communism was finally legalized and the Finnish Communist Party, a strong ally of the USSR, became a powerful force in finnish politics until its decline in the 1980s. Thus, it is thanks to the USSR and its crushing victory in the Continuation War that Finland is a social democracy today and not a fascist regime. Although its slipping back into fascism recently. These historical facts are being denied by the finnish government and historical revisionism openly promoted. Finnish schools teach that Finland was a “wholesom social democracy” and ebil russians invaded them for no reason. There is no mention of the fact that they were literally nazi allies nor of the numerous war crimes Finland committed both during WW2 and the Finnish Civil War.

So yeah, the dude here is honoring his nazi dad basically.