Complex sentence: The Finnish Democratic Republic (also,) was a short-lived (1939--40) puppet government created and recognised only by the Soviet Union, headed by Finnish politician Otto Ville Kuusinen, through which Joseph Stalin planned to rule Finland.
Split into simpler sentences: The Finnish Democratic Republic (also,) was a short-lived puppet government created and recognised only by the Soviet Union. Headed by Finnish politician Otto Ville Kuusinen, Joseph Stalin planned to use the Finnish Democratic Republic to rule Finland.