Complex sentence: In 1603 he inherited the thrones of England and Ireland, creating a Union of Crowns (while the three states retained their separate identities and institutions), and moving the centre of royal patronage and power to London.
Split into simpler sentences: In 1603 he inherited the thrones of England and Ireland, creating a Union of the Crowns that left the three states with their separate identities and institutions. He also moved the centre of royal patronage and power to London.