C. Locate sources that contradict the author's evidence and conclusions.
Notice some of the broad, sweeping claims made by the author, without support from any cited references:
"I think its capital city had the largest population of any city in all world history." All of world history would include modern cities that have vastly more population than any city in ancient Greece.
"I bet its military conquered nearly all of Europe, Asia, and Africa." That didn't happen -- thus no authoritative sources to cite to prove it did.
"I've heard a report that said" ... What report? Where? Cite the source!
A historian would be able to challenge and refute the claims of this author by citing actual, reliable material that contradicts his unfounded claims.