UN

I have to agree with Beth. Cannon history seems to indicate the UN is at
least partially independent and must hold a bit of territory (even if
only
for research stations, military bases, and a few small enclaves) around
human space. And its obvious they've got enough teeth to prevent the big
boys from hashing it out in the Inner System. 

I'd suggest the UN  
i) has ts own citizens
ii) has its own sources of revenue
iii) receives donations (dues) from member states
iv) has enough teeth to patrol the Core very effectively and the inner
colonies effectively enough
v) is limited by tacit agreement of the major powers from extending its
power into the Outer colonies though no doubt that is UN intention
vi) acts by diplomacy where it can, deterrence where it must, violence
where
nothing else works
vii) acts in the outer colonies by some diplomatic and humanitarian
extensions and by <it is suspected> covert action - intelligence
gathering
and an operational capability
viii) might have some tech up their sleeve no one has seen yet - look at
their ships! ;)

I suspect the UN has enough force to make any major player realize that
trying <insert activity> is a bad idea if the UN objects - maybe the
NAC,
NSL and ESU could individually take out the UN, but they know not
without a
mauling and that'd leave them prey to their other neighbours. Plus in a
case
of one-bully, many bystanders the UN could go for help and get two or
three
other powers to whack the crap out of the offender. 

A structure like this would not allow the UN to mess with the outer
colonies, leaving the big boys and their smaller wannabees to settle who
is
the mui macho hombre out in the fringes while the UN keeps the core
worlds
intact, productive, and relatively peaceful. They're like the pressure
cap
that holds things together and prevents the major powers from wrecking
the
Earth. 
This can't be entirely done by an ineffectual organization with no
resources
of its own. 

YMMV.

Thomas Barclay
Software UberMensch
xwave solutions
(613) 831-2018 x 3008