Complex sentence: Instead, Clark emphasizes the unities and coherences between 1660 and 1832, a period he first dubbed the "long eighteenth century," terminology and dating which is now widely accepted in historical academia.
Split into simpler sentences: Instead, Clark emphasizes the unities and coherences of the period between 1660 and 1832. It was he who dubbed it the "long eighteenth century", a periodisation which is now widely accepted in historical academia.