What is the importance of marketing to a nation, individual, or organization?

The importance of marketing is the same for all of these
types of entities.  They must all market themselves so as to project the best possible
image to the world.  By doing so, they will be able to get others to think well of
them.

The type of entity does not matter -- the goal of
marketing is still the same.  A corporation, for example, wants to sell more of its
products.  To do so, it needs people to think well of it.  Therefore it needs to engage
in marketing.  A country wants to have a good image in the rest of the world for
economic purposes and/or for purposes of political power and prestige.  To get such an
image, it needs people to think well of it.  Therefore, it needs to engage in
marketing.

Marketing is always about making the general
public perceive an entity in a positive light.  All entities want to be perceived in
this way and therefore they (when they can) engage in marketing.