Complex sentence: Boucicault's next marked success was at the Princess's Theatre, London in 1864 with "Arrah-na-Pogue" in which he played the part of a County Wicklow, Ireland carman.
Split into simpler sentences: Boucicault's next marked success was at the Princess's Theatre, London in 1864 with "Arrah-na-Pogue". He played the part of a County Wicklow, Ireland carman.