Complex sentence: Geopolitically less important than the continental Moscow-Warsaw gateway, the northerly Finnish ground, isolated by the Baltic sea was a peaceful sidefront until early 1918, but the war between the German Empire and Russia had indirect effects on the Finns.
Split into simpler sentences: Geopolitically less important than the continental Moscow-Warsaw gateway, the northerly Finnish ground, isolated by the Baltic sea was a peaceful sidefront until early 1918. The war between the German Empire and Russia had indirect effects on the Finns.