emerging power

I see China as a growing threat to many/a lot of developed countries on several many fronts.  Changed to avoid repetition of 'many'. You could change the first or second 'many'.

The once undeveloped, poor nation is now emerging as a superpower. The country is also catching up on the global technological race and this was is proven when it launched a man around the Earth several years ago, making it the third nation to send a man into space. The country's GDP ranked sixth worldwide at a little over $10 trillion, about 16 percent of (that of the US) the US's. Developed nations such as the US, the UK, France, and Germany are increasingly depending on cheap products made in China, causing local producers to go out of business and changing the way of life in those nations.

New2grammar

Thank you, Optilang. You just corrected a mistake that I always have problem with. Why does the possive form fail in this example? I understand the US's as the US's GDP

It may not be wrong, and sounds better when there is something after it, such as GDP. I would always use America's in order to avoid it.