Setting design: Diplomacy, espionage, character actions

Howdy all,

I'm contemplating a space opera setting with an "Earth against The
Empire conflict over hundreds of years" premise. The obvious (to me)
activities for the PCs include military campaigns and free traders;
however, the idea of diplomatic and espionage activities seems
interesting enough to explore.

My trouble is, I know very little about how these things work in the
real world, or even in fiction. What works should I be referencing for
state-level diplomacy as a thrilling adventure? For espionage that is
actually related to real intelligence-gathering by groups of people
(unlike, say, James Bond)?

My main concern is to combine a convincing-enough feel of top-level
diplomatic negotiation and covert activities, but with enough things
for the player characters to do that they can feel they're having a
real effect on the process.

-- 
 \        "Intellectual property is to the 21st century what the slave |
  `\                           trade was to the 16th."  -- David Mertz |
_o__)                                                                  |
Ben Finney