Complex sentence: Situated in a predominantly Royalist area of the country, the estate and castle were vulnerable to attack, but notwithstanding this Robert Harley left the defence of the castle in the hands of his remarkable wife, Lady Brilliana Harley.
Split into simpler sentences: Situated in a predominantly Royalist area of the country, the estate and castle were vulnerable to attack. This notwithstanding, Robert Harley left the defence of the castle in the hands of his remarkable wife, Lady Brilliana Harley.