You can read part I here.
Ancient China and much of Asia saw widespread use of spies and espionage during its turbulent history. In fact, the use of these agents was so common that the final chapter of Sun Tzu’s “The Art of War” (Sunzi Bingfa) is dedicated to spies, spying, and their importance in battlefield and political tactics. One passage from the treatise actually equates the neglect in utilizing spies to a form of inhumanity, stating:
“Hostile armies may face each other for years, striving for the victory which is decided in a single day. This being so, to remain in ignorance of the enemy’s condition simply because one grudges the outlay of a hundred ounces of silver in honors and emoluments, is the height of inhumanity.”
Military and political leaders heeded the advice, making extensive use of spies for everything from determining enemy position and status to rooting out (and sometimes launching) coups. In addition to advocating the utilization of spies and espionage, Sun Tzu even went so far as to break down the type of spies that a commander might have at his disposal, as well as advice for commanders on how to best handle them. The types of spies noted include: