Complex sentence: Soon afterwards they moved to Vienna, where James, an admirer of Freud, began a psychoanalysis with the great man, something which he would claim to Lytton "provided" a complete undercurrent for life "".
Split into simpler sentences: Soon afterwards they moved to Vienna, where James began a psychoanalysis with Freud, of whom he was a great admirer. He would claim to Lytton that his analysis "provided" a complete undercurrent for life "".