Thanks for your explanation.

The sentence I quoted is confusing simply because you use 'they' to reference both the USA and China .

Thank you for the details you have provided because that makes your analysis much clearer.

With respect perhaps you could be more specific . You say. The world's nuclear power program began in 1953. Why does the USA represent the world? I'm assuming you mean the world's first nuclear program, was initiated by the Americans (with an international team of physicists by the way).

The second sentence is also a bit unclear - why not say, China 's first independently designed .... etc etc...

It's helpful to be more precise rather than using the passive form. You don't need to write at length, but to write with more precision. This is where an editor helps a lot, because you as a specialist have a lot of knowledge you wish to share, so it's harder for you to have , 'beginner mind'!