Complex sentence: When about a quarter of the Chu army had crossed the river, Han Xin signalled for his men to open the dam, drowning many Chu soldiers and isolating Long Ju with only a fraction of his forces.
Split into simpler sentences: When about a quarter of the Chu army had crossed the river, Han Xin signalled to his men to open the dam. Many Chu soldiers drowned and Long Ju was isolated with only a fraction of his forces.