Complex sentence: This unexpected reprieve, however, led to a brutal death march: for the next week, the prisoners were forced by SS soldiers wielding wooden clubs and steel bars to march 21 miles a day at top speed.
Split into simpler sentences: This unexpected reprieve, however, led to a brutal death march. For the next week, the prisoners were forced by SS soldiers wielding wooden clubs and steel bars to march 21 miles a day at top speed.