Complex sentence: The Alleged Lunatics' Friend Society (ALFS) was a pressure group started by ex-patients in 19th century Britain that campaigned for the human rights of people alleged to have mental disorders (who were known then as lunatics).
Split into simpler sentences: The Alleged Lunatics' Friend Society (ALFS) was a pressure group started by ex-patients in 19th century Britain. The organisation campaigned for greater human rights for people alleged to have a mental disorder (who were known then as lunatics).