Complex sentence: The German inhabitants of Stettin first fled from the city that were virtually deserted after being captured by Soviet army on Apr 26,1945, but later returned as it was undecided if the city would be in Poland, or in the Soviet occupation zone in Germany.
Split into simpler sentences: The German inhabitants of Stettin first fled from the city and it was virtually deserted after being captured by Soviet army on Apr 26,1945. Later, they returned, as it was undecided if the city would be in Poland, or in the Soviet occupation zone in Germany.