Here is a link to Lev Gumilev's book (in English) which serves as a basis for the socionic hypothesis of national types:

http://gumilevica.kulichki.net/English/ebe.htm

Lev Gumilev (or Gumilyov, Gumiliov) was a historian who studies similar tendencies in the history of different nations and discovered certain regularities, rhythms of development, which allows developing scientific criteria of distinguishing one nation from the other, even when they speak the same language (like Austrians and Germans, Serbs and Croatians).