Complex sentence: During the battle on a moonlit night Douglas was killed, his death had no influence on the outcome of the battle and went unnoticed until much later, the Percys were both captured, with the remaining English force retreating to Newcastle.
Split into simpler sentences: During the battle on a moonlit night Douglas was killed; his death had no influence on the outcome of the battle and went unnoticed until much later. The Percys were both captured, with the remaining English force retreating to Newcastle.