Good question. We don't have either the resources or the obligation to put troops in every savage corner of the world. A private effort to buy a few thousand bolt action surplus rifles and ammo and deliver them in modest size batches to the oppressed population might be the best that could be hoped for.
The UN is of course useless or worse.
Usually the UN can be expected to do everything short of actually helping the people in these sorts of situations, but in this case they've done nothing, not even issued a strongly-worded condemnation.
The Sudan's been spending big on hi-tech that you know is over their head. Destroy it. If they persist in the south hit the palaces. The alternative is hand-wringing and finger pointing five years from now ala Rwanda and Clinton.
Yes, you're right, but that is illegal, as it is considered operating an independent foreign policy of the U.S.
It was these constraints which were at the root of the Iran-Contra fiasco; the attempt to arm the Contras in Nigaragua after the U.S. Congress denied them aid.
I'd love to have the money and ability to run my own foreign policy.