According to the author of Guns, Germs, and Steel, why is writing an agent of conquest?Found in Chapter 12: Blueprints and Borrowed Letters

Writing is an agent of conquest because it is the most
efficient way to convey and to store large amounts of
information.

Information is very important.  Information
can help fleets of ships know where to go as they head off to conquer and colonize.  It
can tell them what they need to know about the areas they are going to try to conquer. 
Information can also help to organize the fleets and the armies that are needed to
conquer.  Taking a step back, writing even helps to collect the tax revenues that are
needed to fund these fleets and armies.

Information is
power.  Writing is a good way to accumulate information and to pass it from person to
person.  For these reasons, writing is an agent of conquest.