Complex sentence: It was created in 1703 for David Boyle, Lord Boyle, who was subsequently one of the commissioners who negotiated the Treaty of Union uniting the Kingdom of England and the Kingdom of Scotland into the Kingdom of Great Britain.
Split into simpler sentences: It was created in 1703 for David Boyle, Lord Boyle. The first earl was subsequently one of the commissioners who negotiated the Treaty of Union uniting the Kingdom of England and the Kingdom of Scotland into the Kingdom of Great Britain.