"[P]erhaps it is not too late to advance a view that, I believe, is not only mine alone but is shared by a number of others with extensive and in most instances more recent experience in Russian matters. The view, bluntly stated, is that expanding NATO would be the most fateful error of American policy in the entire post-cold-war era. Such a decision may be expected to inflame the nationalistic, anti-Western and militaristic tendencies in Russian opinion; to have an adverse effect on the development of Russian democracy; to restore the atmosphere of the cold war to East-West relations, and to impel Russian foreign policy in directions decidedly not to our liking."
January 1, 1970
https://en.wikiquote.org/wiki/George_F._Kennan