Complex sentence: Historically and at the present day, significant unionist movements exist in Scotland and Northern Ireland seeking to retain the ties between those areas and the UK in opposition to separatist nationalist movements such as the Ulster Unionist Party and the Scottish Unionist Party.
Split into simpler sentences: Historically and at the present day, unionist movements exist in Scotland and Northern Ireland seeking to retain the ties between those areas and the UK, in opposition to separatist nationalist movements. These include as the Ulster Unionist Party and the Scottish Unionist Party.