You know I just thought of this, but with enough Nukes going off at the same time in roughly the same general place on the globe. The earth could have been moved out of the orbit we know of today. It could possibly have gone into a more elipical orbit with the sun, a closer orbit with the sun(which would the extreme heat and desert conditions), it could have gone into a spiraling orbit.
With enough force exerted in one place, nuclear explosions would act the same as a booster rocket on a space ship. "With every action, there is an equal and opposite REACTION" The force of the explosions would push upon the atmosphere and then upon the magnetosphere and then upon solar radiation in space and thereby actually moving the earth out of it's standard orbit.
Even if all the nuclear weapons weapons in the world wold be detonated now this wouldn't happen. Is basicly impossible to do with just a "couple" of nukes.....
Back to the Topic.
Midle-east and Europe were preaty much already destroied because of a prolonged war for the remaining oil BEFORE the Great War so with all the chaos and problems they already have they wouldn't have the resources to also send nuclear weapons, plus they wouldn't realy care about US and China blowing up eachother... Comon just think a bit, if i was an US ally and sudenly a nuclear-war that will devastate both US AND theyr enemyes wy would i involve myself? I would put some burocratic issue ("My congress/parlament is being reunited in this moment to discuss the matter Mr. US President!") and wait for some few hours, in the end of the day with both super-potencies reduced to ashes i realy doubt they would take any action agains my selfish action...
Now i agree that most infrastructure on the Europe, Oceania, AFRICA AND SOUTH AMERICA (people tend to forget these two places) would be preaty much intact. However there is the effects that only happens AFTER the bobms drops, in either way even the most "intact" areas would become a dry wasteland after 3 or 4 years, and chaos would had already made those places suffer a lot of losses after the first few monts. So i do belive that the rest of the world (South America. Europe, Oceania, Africa and a portion of the western most asiatic countrys) should have become a wastlands with completely diferent caracteristics of the US/China ones. IMHO those countrys or atleast a portion of them, must have survived the post-apocaliptic war and are still learning how to deal with the new world they live in. They might actualy much more stronger than any of the old super-potencis with far more advanced tecnologi. And before people start to question this line of thoutgh asking why they dont help the countrys that suffered a direct hit from the bombs, there is an extremely TWO simple answer to this, first THEY DONT CARE and second they are too busy adapting to the new world to even think about it....