Complex sentence: From 1809 to 1898, a period called "Pax Russica", the peripheral power of the Finns gradually increased, and the Russian-Finnish relations were exceptionally peaceful compared with other parts of the Russian Empire.
Split into simpler sentences: From 1809 to 1898, a period called the "Pax Russica". Finnish-Russian relations had been exceptionally peaceful and stable compared with other parts of the Russian Empire.