 Brooks conducted copious research while writing World War Z. The technology , politics , economics , culture , and military tactics were based on a variety of reference books and consultations with expert sources . Brooks also cites the U.S. Army as a reference on firearm statistics . 
 Brooks conducted copious research while writing World War Z. The technology , politics , economics , culture , and military tactics <a href='uninflect' title='1'><mark>were</mark></a> based on a variety of reference books and consultations with expert sources . Brooks also <a href='uninflect' title='2'><mark>cites</mark></a> the U.S. Army as a reference on firearm statistics . 
Brooks conducted copious research while writing World War Z. The technology , politics , economics , culture , and military tactics was based on a variety of reference books and consultations w expert sources . Brooks also cite the U.S. Army as a reference on firearm statistics .