I was asking a question, so I was looking for an explanation. Honestly, I am not sure what form international observers would take.
Observers in China, perhaps on the US/Mexican border, and wherever oppression against civilian populations occurs would be difficult, often impossible, but seems like it would be worth the effort.
China and the US would never allow foreign troops on their soil, even if they're from the UN. As superpowers and permanent security council members, they're the ones who dictate where UN peacekeepers go.
If you're talking about a non-militarised observer, I'd say that role is supposed to be filled by journalists. But all of these countries go to great lengths to keep journalists away from their atrocities.
Observers in China, perhaps on the US/Mexican border, and wherever oppression against civilian populations occurs would be difficult, often impossible, but seems like it would be worth the effort.