Complex sentence: Li Xubin had to retreat back to the forts with the surviving imperial troops in an attempt to hold their positions and await reinforcements, however the 15,000 men of the imperial Green Standard Army were delayed and played no part in the battle.
Split into simpler sentences: Li Xubin had to retreat back to the forts with the surviving imperial troops in an attempt to hold their positions and await reinforcements. However, the 15,000 men of the imperial Green Standard Army were delayed and played no part in the battle.