In the sixth chapter, Freud reviews the development of his concept of libido to explain why it must now be separated into two distinct instincts: the object-instinct of eros and the ego-instinct of thanatos. This 'new' concept of the death drive actually has a long developmental history in Freud’s writings, including his investigations into narcissism and sadomasochism. Freud admits it may be difficult to accept his view of human nature as being predisposed towards death and destruction, but he reasons that the suppression of this instinct is the true cause behind civilization's need for restrictions. Life and civilization, then, are born and develop out of an eternal struggle between these two interpersonal forces of love and hate.