Complex sentence: During the Victorian and Edwardian era, in America "morning coat" referred to a single-breasted frock coat, so the British then made fun of the fact that Americans were unable to distinguish between morning coats and frock coats.
Split into simpler sentences: During the Victorian and Edwardian era, in America morning coats were referred to a single-breasted frock coat. During this period, the British often made fun of the fact that Americans were unable to distiguish between morning coats and frock coats.