Complex sentence: Diesen was a journalist for the newspaper "Aftenposten" from 1921, and served as editor-in-chief for "Aftenposten" from 1948 to 1968.
Split into simpler sentences: Diesen was a journalist for the newspaper "Aftenposten" from 1921. He served as editor-in-chief for "Aftenposten" from 1948 to 1968.