Complex sentence: During Mary's reign, the Countess of Lennox had rooms in Westminster Palace; but on the accession of Queen Elizabeth I, she moved to Yorkshire, where her home at Temple Newsam became a centre for Roman Catholic intrigue.
Split into simpler sentences: During Mary's reign, the Countess of Lennox had rooms in Westminster Palace. On the accession of Queen Elizabeth I, she moved to Yorkshire, where her home at Temple Newsam became a centre for Roman Catholic intrigue.