Complex sentence: The regiment remained in England for nearly three years before it saw battle again, recruiting to refill its ranks and also losing Colonel Leveson when he was promoted to the rank of Major-General by King William.
Split into simpler sentences: The regiment remained in England for nearly three years before it saw battle again. During this period, in which it recruited to refill its ranks, it lost Colonel Leveson when he was promoted to the rank of Major-General by King William.