Friedrich was formerly considered a left-wing antiwar activist and described as a student Trotskyist. His books have sold hundreds of thousands of copies in Germany, and some have also been translated into English, Dutch, French and many other languages. He is well connected in German political and military circles and is a friend of former German Chancellor Helmut Kohl. He has published interviews with Rudolf Bahro and Raul Hilberg when their books were published. His new book "14/18 Der Weg nach Versailles" focusses on the First World War.