Also something that was gnawing at me since I first posted, and something I'm hoping OP has considered: not everyone buries their dead and most often the funerary rights of other cultures totally destroy the body.

For instance: China now-a-days REQUIRES you cremate your dead. At least among the Han majority. Groups like the Hui get a free pass because of their Muslim beliefs, which strictly forbid the cremation of the dead.

Like wise in the area, Tibetan tradition dictates that a body is to be chopped up and literally fed to the vultures in a process known as sky-burial. So China and Tibet shouldn't have any bodies when it comes to main-land Asia; apart from a few minority groups there's no bodies in China any more to raise up from the dead, they keep burning them.

Same in India across the Himalayas. Although cremation isn't strictly enforced and there is a cheap alternative to cremation called, "Throwing uncle Raj in the river". But cremation in India is heavily practiced and is encouraged by the Hindu, Sikh, and Jainist faith. It's like-wise encouraged in Buddhism but not as heavily as the Hindus. So they'd be having a living-corpse deficit from within the borders to be a strict threat.

The Japanese also often cremate their dead.

This may sound like it's completely defeating the purpose of the RP, but if the source of this mass-rising of the dead is originating for "Christian" western countries and the Muslim world then it can be strongly argued that as a whole that'd be enough damage to devastate the world economy and draw India and China back, in addition to Japan (if Japan isn't being swarmed from any native corpses buried under Christian rights).

But I'm pretty sure the Chinese or the Indians wouldn't have failed as a state given their large nations with a considerable amount of living people and they could hold off anyone coming. The "shock" might be when the recently deceased get back up and start killing things. But a morgue can be easily locked tight and the whole thing torched to the ground. Then demand everyone torch their dead a lot sooner.

We can still preserve a sort of apocalypse scenario in the US though. It's just a qualm with the wider lore. Some manner of quarantine placed on the world from Asia way can keep the status quo and likely make Hindustan and China sort of legends in their own right for the possibility they may still exist.