Independence and Civil War (1917–18)
During the wake of February Revolution, the position of Tsar as the Finnish head of state was highly questionable, especially the Social Democrats who had a majority in the Senate. Finland considered the personal union with Russia to be over after the dethroning of the Tsar, and Tsar's authority was expected to be transferred to Finland's Parliament, which the provisional government of Russia refused, suggesting instead that the question should be settled by the Russian Constituent Assembly.
The Social Democrats proposed to restrict Russia's influence on domestic Finnish matters while retaining the Russian government's power on matters of defense and foreign affairs, famously known as the "Power Act". The Russian Provisional government considered the Act being too radical, led to the dissolve of Parliament of Finland. The non-Socialists was supporting the provisional government's step, in the fear of the growing influence of the Social Democrats.
New elections were conducted, in which the non-Socialists won a slim majority. The Finnish Senate now was purely under the control of non-Socialist forces. The suppression of the Power Act and the cooperation between Finnish non-Socialist forces and Russia provoked great bitterness among the Socialists, which later triggered the conflict between these two political forces.
The October Revolution of 1917 turned Finnish politics completely opposite from before. As in the Ukraine, the new Finnish non-Socialist majority of the Parliament desired total independence, and the Socialists came gradually to view Soviet Russia as an example to follow. On November 15, 1917, the Bolsheviks declared a general right of self-determination, including the right of complete secession. On the same day, the Finnish Parliament issued a declaration by which it temporarily took power in Finland.Worried by the political development in Russia, the non-Socialist Senate proposed that Parliament to declare Finland's independence, which was agreed on in the Parliament on December 6, 1917. On December 18, 1917 (December 31 N. S.), the Soviet Russian government issued a decree that recognizing Finland's independence, and on December 22, 1917 (January 4, 1918 N.S.) it was approved by Soviet's All-Russian Central Executive Committee. The German Empire followed the recognition of Finland immediately.
However, the tension between the Finnish working class, known as the Reds, and the Finnish peasantry, conservatives and Swedish-speaking minority, known as the Whites, worsened. The brief, but bitter, Finnish Civil War was sparked between January and May 1918. World War I was still underway and Imperial Germany declared its support to the Finnish White forces, while Scandinavia chosen to remain neutral during the conflict and Russia withdrew its forces. The Reds was finally defeated by the White forces under the command of Carl Gustaf Emil Mannerheim.
Interbellum era (1918–39)After the civil war, the Parliament, now controlled by the Whites, voted to establish a constitutional monarchy with Frederick Charles of Hesse as the king. However, the armistice between the belligerents of World War I was signed on November 11, 1918. Not much is known of the official stance of the victorious Allies regarding the possibility of a German-born prince as the King of Finland. Frederick Charles renounced the throne on December 14, 1918. Another candidate, Carl of Denmark, was selected instead with the support from the conservatives, especially from its Swedish-speaking elements.
Prince Carl was crowned as the King of Finland on February 25, 1919 (March 10 N. S.) with the regnal name Charles I of Finland (Finnish: Kaarle I). During his reign, King Charles I gained much sympathy from the Finnish people. Thanks to the popularity of the monarchy, Finland becomes and remains a parliamentary democracy until today despite a bitter civil war and several foreign invasions. Finland also did not see any leftist coup attempts and survived the anti-communist Lapua Movement during the interbellum era. This political stability and national unity later showed its importance during critical moments such as the Winter War in 1939-1940.
In 1939, facing the imminent Soviet invasion, the Estonian Parliament declared the establishment of Kingdom of Estonia with King Charles I as the first monarch. The declaration thus created a personal union between Estonia and Finland. Although Charles I did not accept the declaration readily at that time, Helsinki and Tallinn immediately created a common Finnish-Estonian army under a single command nominated by the governments of two countries. A following merger aimed to have Estonia and Finland as one country was proposed by the Estonian government. The proposal, however, was cut short by the Soviet invasion.
Winter War (1939–40)By early 1930s, a small but powerful element within the Soviet Bolshevik Party advocated the reconquest of the provinces of Tsarist Russia lost during the October Revolution and the Russian Civil War. This faction then gained significant support from several party leaders after the New Opposition assumed power in 1934. The Soviets believed that the old empire had ideal security and territorial possessions. Leningrad regional party leader, Sergei Kirov, demanded the Soviet-Finnish borders be revised since his region was only 32 km from the Finnish border and wanted to guarantee Leningrad's security from the possible Finnish attack.
In early 1939, this pro-war faction gained a majority on the AUCP Central Committee, thus driven the Soviet policy more toward the establishment of buffer zone between Germany and the Soviet Union following the failure of collective security policy. When the Red Army pre-emptively invaded the Ukraine on September 17, 1939 following the German invasion of Poland sixteen days earlier, it was clear for the Finnish leadership that the Soviets soon or later will expanding military conflicts into the Baltic states and Finland.By October 1939, the Soviets and the Finns exchanged diplomatic negotiations regarding the modification of Soviet-Finnish border. However, the negotiations were unable to find a common agreement between two countries, thus signaled the beginning of Baltic conflict. On November 30, 1939, the Soviet Red Army invaded Finland and Estonia, signaled the beginning of the Winter War. Carl Mannerheim was appointed Commander-in-Chief of the Finnish-Estonian Defence Forces by Charles I following the invasion.
Even though the Soviet Red Army had huge superiority in men, tanks, guns, and airplanes, the Finns and Estonians were able to maintain their defense about 3.5 months. The Soviet invasion also did not gain support from the Finnish working class who stood behind the legal government in Helsinki. Finnish national unity against the Soviet invasion was later officially glorified by the state as the "Spirit of the Winter War". The Winter War ended on March 13, 1940 with the Moscow Peace Treaty. Finland lost the Karelian Isthmus to the Soviet Union after the war.