During Middle Ages, the Swedish kingdom is in a middle of a conquest and also is christianizing Finland.
Finland served few times of battlefield for battles between Swedish and Russian empires.
In 1809, Finland becomes a Russian Grand-Duchy.
In 1917, taking benefits from the mess caused by the Bolshevik revolution, Finland declares its independence. We have to mention Finland's independence has only been recognized in 1918 due to political conflicts which led to a civil war between Reds and Whites (2 former opposite sides). Whites finally won.
In 1939 due to the Molotov-Ribbentrop agreements, the Soviet Union imposes an ultimatum to Finland and finishes attacking Finland because the demand was rejected by the country. This is the Winter War of 1939-1940. Finland will find itself reduced of 10% but will stay independent contrary to Baltic countries.
In 1941, Finland attacks the Soviet Union to recover its lost territories. However, Finland decides to stop the offensive in lake Onega, and will never cut the line of Murmansk neither attack Leningrad even though Hitler ordered them to do so.
In 1944, Finland withdraws to the former border under the Soviet pressure. Finland signs an armistice with USSR providing the German Army's leaving of the country. The army was based at the North of the territory. Its failed evacuation triggered Lapland War against the Germans.
The conditions made in 1940 got harder due to the armistice.
After War, the Paasikivi line of strict neutrality turns Finland in a meeting point of relations East-West.
Finland joins the European Union in 1995.