Complex sentence: Because of Stanley's delays, the rear column was to remain at Yambuya, by the Aruwimi River for the next 14 months, rather than 4, by which time two of its officers and over 100 of its porters had died.
Split into simpler sentences: Because of Stanley's delays, the rear column remained at Yambuya by the Aruwimi River for the next 14 months, rather than 4. By that time, two of its officers and more than 100 of its porters had died.