Complex sentence: The diaries are considered to be authentic and to provide actual details of the brothels and the lives of comfort women because the author died before the issue of comfort women was not yet the source of tensions between Japan and South Korea.
Split into simpler sentences: The diaries are considered to be authentic and to provide actual details of the brothels and the lives of comfort women. The author died before the issue of comfort women was a source of tensions between Japan and South Korea.