Complex sentence: Accordingly, by midafternoon, the rear of the column--believing the day's march to be nearly at an end--was dawdling; this resulted in the army becoming separated, with some having already crossed the summit and others still approaching it.
Split into simpler sentences: Accordingly, by mid-afternoon, the rear of the column--believing the day's march to be nearly at an end--was dawdling. This resulted in the army becoming separated, with some having already crossed the summit and others still approaching it.