Republic of Finland
Who & why: as Russia's Provisional Government stalls on granting real autonomy and the Bolsheviks then seize power in Petrograd, Finland's senate under P. E. Svinhufvud moves fast: parliament declares independence on 6 December 1917, and Lenin's new Soviet government recognizes it within weeks, on 31 December — partly on principle, partly because it has far bigger problems at home. Independence is immediately tested: a brief, bitter Civil War between the socialist "Reds" (based in Helsinki, loosely backed by Soviet Russia) and the conservative "Whites" (the Senate's forces under General C. G. E. Mannerheim, aided by a German expeditionary corps) runs from late January to May 1918, leaving deep scars but a White victory and an intact state. That autumn, a German-leaning majority in parliament briefly elects a German prince, Frederick Charles of Hesse, as King of Finland — a plan that collapses within weeks when Germany itself loses the war, and Frederick Charles never takes the throne. Finland settles the question for good with a republican constitution, ratified 17 July 1919, and its first elected president, K. J. Ståhlberg. Sovereignty is defended again, without being lost, in two later wars against the Soviet Union: the Winter War (1939–40) and the Continuation War (1941–44) both end with Finnish territory ceded but Finnish independence intact — the only mainland European country bordering the USSR in 1939 that was never occupied.
What it represents: a white field for the snow, a blue Nordic cross echoing the country's thousands of lakes — blue and white had already been informally popular as "Finland's colors" from the late 19th century onward. Parliament formalizes this exact design on 29 May 1918, right in the middle of the Civil War's aftermath, deliberately choosing a plain civil cross over any crown, eagle, or dynastic emblem.