February 21, 1808: The Russian army invaded Finland, despite not having declared war on the Kingdom of Sweden. The war was over by the end of March, leaving Finland an autonomous Grand Duchy in the Russian Empire until 1917.
There were actually several Finnish mapiversaries to choose between today. It was a toss-up between the beginning of the Finnish War, the 1245 resignation of the first known Bishop of Finland, or the 1914 birth and interestingly-timed 1999 death of Finnish ace pilot Ilmari Juutilainen.
Either way, quite a day for the Finnish.
Map: Coronelli, Vincenzo. L’Evrope: selon les mémoires les plus nouveaux/ dressée par le P. Coronelli…; corrigée par le S. Tillemon … Paris: I.B. Nolin, 1696