Complex sentence: He had originally sought the backing of the local Unionist association which happened to be called the Westminster Abbey Constitutional Association, so he adopted the term'Constitutionalist' to describe himself during the by-election campaign.
Split into simpler sentences: He had originally sought the backing of the local Unionist association which happened to be called the Westminster Abbey Constitutional Association. He adopted the term'Constitutionalist' to describe himself during the by-election campaign.