Complex sentence: Once these loyal lords were removed from Narnia, Miraz allowed himself to be proclaimed King by his own followers, having already placed them into high office as part of his scheming to be accepted as King.
Split into simpler sentences: Once these loyal lords were removed from Narnia, Miraz allowed himself to be proclaimed King by his own followers. He had already placed theses followers into high office as part of his scheming to be accepted as King.