Microbial invasion--the major ally of war (natural biological warfare).
D001424:Bacterial Infections / Q000266:history*; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D008887:Military Medicine / Q000266:history*; D010272:Parasitic Diseases / Q000266:history*; D014481:United States; D014777:Virus Diseases / Q000266:history*; D014857:Warfare