Complex sentence: Any attempt to turn Wellington's right would entail taking the entrenched Hougoumont position; any attack on his right centre would mean the attackers would have to march between enfilading fire from Hougoumont and La Haye Sainte.
Split into simpler sentences: Any attempt to turn Wellington's right would entail taking the entrenched Hougoumont position. Any attack on his right centre would mean the attackers would have to march between enfilading fire from Hougoumont and La Haye Sainte.