“We’re caught in a trap,” Elvis Presley sang in “Suspicious Minds.” The trap then was jealousy. The trap everyone is talking about now — even China’s Xi Jinping found it of use — is the so-called “Thucydides trap.” Thucycides wrote the classic history of the Peloponessian War. Yale’s late, great teacher Donald Kagan wrote a four-volume history of the Peloponnesian War that is a standard in the field. All four volumes have been kept in print by C…