What was Finland's position in World War Two? Apparently, they were fighting against the Soviet Union, but not as Nazi Germany's ally. Are there reasons for this, and were they actually on Germany's side?
The USSR attacked Finland in 1939, which ended in a stalemate (1940). This was an embarrassment to the USSR, but the treaty gave the USSR 10% of Finnish territory.
Finland sought to bolster its military strength with treaties and alliances. Great Britain and the USA were allied with the USSR against Hitler at the time and therefore would not help. Finland turned to Germany (the enemy of my enemy is my friend...), which sent troops to Finland.
In June of 1941 the USSR launched air-raids against Finland, which in turn declared war on the USSR and allowed German troops stationed within Finland to take offensive action. In the south the Finns and Germans re-took their territory. When they started going beyond reclaiming land, the UK demonstrated its support of the USSR with its Raid on Kirkenes and Petsamo. In December 1941 Finland took up defensive positions, which resulted in relative calm for several years.
On 16 March 1944, the President of the United States, Franklin D. Roosevelt, called for Finland to disassociate itself from Nazi Germany.
On 9 June 1944, the Red Army launched a massive attack against Finland.
The USSR pushed the Finns back to where the previous truce had occurred (-10% land for Finland).
The dire situation in 1944 had led to Finnish president Risto Ryti giving Germany his personal guarantee that Finland would not negotiate peace with the Soviet Union for as long as he was the president. In exchange Germany delivered weapons to the Finns. After the Soviet invasion was halted; however, Ryti resigned.
The USSR was then in a race to Berlin and couldn't be bothered with Finland. In Sept 1944, peace was made and the Moscow armistice signed, which bound Finland to drive German forces from Finland. Finland tried to drive the Germans in a friendly fashion; agreeing to let the Germans leave peaceably. The Soviets refused to accept that, and so Finnish troops attacked the Germans, who proceeded to burn most of the houses in the Northern half of Finland (1-2k casualties on each side, and 100,000 people lost their homes).
Note: Finland protected its Jews against the Nazi's antisemitism.
Finland to an extent played both sides. This article pretty well covers things. The combination of difficult terrain and well trained, well equipped soldiers helped the Finns ensure their independence. They did lose a fair chunk of territory to the Soviets but succeeded in staying masters of their own affairs and allegiances.
Joe Hobbit summarises the bulk of the war, but it is important to note that during the Winter War (1940), the Soviets were collaborating with Germany, and not yet allies with UK or France.
In fact, UK and France tried to send military support to Finland, and many volunteers actually fought alongside the Finns.
Basically, Finland was caught in the middle of events much larger than themselves. They wanted to defend themselves, and allied with whoever was opposed to the Soviets at the time.
Finland had lost "11% of its territory and 30% of its economic power" (e.g. the Petsamo nickel mines to the Soviet Union in the "Winter War" of 1939-1940.
The German invasion of the Soviet Union offered Finland a chance to get these back. Finnish troops advanced to the pre (Winter) war boundary, but no further.
Finland wasn't pro Nazi Germany. But "the enemy of my enemy is my friend."
Finland had a military treaty with Germany and they commonly prepared operation Barbarossa (invasion in the USSR). German army prepared positions on Finnish territory and Finnish army started mobilization 15 June, a week before the invasion in the USSR had started.
10 July 1941 Finnish army together with German troops stationed in the Finnish territory began offensive in the USSR.
On the occupied territories Finnish administration created concentration camps for Slavic-speaking population and performed ethnic cleanings. On the other hand Permic and Ugic-speaking peoples were respected.
Jewish POWS and Soviet citizens were separated in special camps for Jews with moderate regime. They were planned to be transferred to Germany about which they were informed, although only a minority of POWs were actually transferred to Gestapo (mostly Communists irrespective of ethnicity).
In the Soviet territory Finnish troops also participated in the siege of Leningrad.
In 1944 after the armistice with the USSR Finland declared war on Germany and expelled German troops.