Spykman, Nicholas John. <br/><br/>
Frontiers security and international organization. 

 - New York-US :   Geografical record,   1942. 
 - páginas 436-447 :   Ilustraciones blanco y negro 
 - Irregular 
 - Vol. XXXII, no. 3(Jul. 1942) 
 - The Geographical Review ;   no. 3 .
 - The Geographical Review. .