Complex sentence: By the 20th century, Nunney Castle was increasingly ruined and covered in thick ivy; as a result, on 25 December 1910 a portion of the damaged north wall entirely collapsed--most of the fallen stone was stolen by local people.
Split into simpler sentences: By the 20th century, Nunney Castle was increasingly ruined and covered in thick ivy. As a result, on 25 December 1910 a portion of the damaged north wall entirely collapsed--most of the fallen stone was stolen by local people.