I'm the only one that doesn't think they're a threat..
In politics there are no eternal friend or foe. Of course Russia is selling arms but not to muslims in general, Countries.
Chechnya is a muslim province that has plotted many terrorist acts against the Russians, The school in Beslan, the Moscow Theatre etc.
The Russians have fought against the Mongols and Turks. Trust me if anything happens Russia will shut them all down.
As for China, I don't see them as a threat to Serbia ( since I'm a Serb), But for America who knows. I mean you bombed their embassy in Serbia. That's not very friendly:P
They support the Serbian side in the Kosovo conflict and they are against north Korea's nuclear arms. Although they were allies before.
So I just think that China will be a Superpower, but not necessarily in war against USA.