Complex sentence: The Hungarian, Italian and Romanian armies were from Stalingrad, which was in range of forward air bases and "Luftflotte" 4 attacked the city, turning much of it to rubble.
Split into simpler sentences: The Hungarian, Italian and Romanian armies deployed for this task were now from Stalingrad, which was also within reach of forward air bases. Consequently, bombers of "Luftflotte" 4 attacked the city, turning much of it to rubble.