The major players are simply too interconnected to risk a direct conflict between them. China for example owes a lot of it's economy to western nations buying it's cheaply-made goods. Because of this no matter how much of our debt they own (which for the record is only about 8%, the highest single owner by a significant margin but not even close to a majority) they are at least as dependent on us as we are on them.
I could see a significant regional war, most likely in the Middle East, but again the major players are going to avoid direct confrontation even if they technically support different sides.
In other cases like North Korea, a new war would simply be about a dozen different nations dog-piling North Korea while China, after being assured of their own security via diplomatic channels, looks the other way. The war would last maybe a couple of months at most, mere hours if nuclear weapons are deployed.