Complex sentence: He was awarded the Knight's Cross in December 1943, for his actions in the Dnieper sector in October 1943, the Russians had succeeded in building a bridgehead in the area of Kanev which threatened the whole corps.
Split into simpler sentences: He was awarded the Knight's Cross in December 1943, for his actions in the Dnieper sector in October 1943. The Russians had succeeded in building a bridgehead in the area of Kanev which threatened the whole corps.