Seath:

Thats a pretty good vid.
I think I will try my shot at one like this eventually...

 

UNSC stands for United Nations Space Command, which was formed as a military organization during the interplanetary wars. During the interplanetary wars, two organizations opposed the United Nations, however, they were defeated.

The aftermath of the war saw the entire world incorporated into the United Nations. Theoretically speaking, nations still exist, but with greatly limited power and serving on a sort of congress(the UN)

The UNSC is just the Space-Borne branch of the military.
There are still other forces such as the Army(although, they may also be incorporated into the UNSC)

I know this has nothing to do with the topic but "Seath" where did you get that picture of yours and what is it?

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marine:grenade out!
grunt:I caught it!
elite:*sigh*
BANG