Complex sentence: The goal of Swedish warfare during the 17th century was to make the Baltic Sea an all-Swedish sea ("Ett Svenskt innanhav"), something that was accomplished except the rout between Riga in Latvia and Szczecin in Poland.
Split into simpler sentences: The goal of Swedish warfare during the 17th century was to make the Baltic Sea an all-Swedish sea ("Ett Svenskt innanhav"). Something that was accomplished except the rout between Riga in Latvia and Szczecin in Poland.