system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is it commonly predicted that China will become the World's biggest superpower?

On the one hand they're communists, right? On the other hand, the US is hugely in debt to them (how did that end up happening?).

And in the modern era where there's much more openness and ease of access between different lands, how will China's status be felt?
gpt
China has a billion people in it, has the second largest economy in the world, and if their growth rates keep up, they'll surpass the US before much longer. This is why people are afraid.

Of course, the exponential growth isn't really sustainable, a huge segment of the population is in abject poverty, the demographics situation is pretty bad, and there's a lot of racial and political tension in the country as well. They also lack any real naval or air power, and don't have anywhere near as many nuclear weapons as the US does. Even if they did start to aggressively militarize, they'd be perpetually playing a game of catch up. This is why the fears are unfounded. 

China's a growing power to be sure, but there is still an absolutely massive gap between the US and China. Even if the status quo for Chinese growth remains, the US will unquestionably be on top for decades, and will at the very least be a serious contender for the top spot in global politics for the foreseeable future. 

Also, to address your first question, China's not really all that communist anymore. They're still run by the communist party, but it's really communism in name only. As for the debt, not only is debt not bad, the overwhelming majority of American debt is owned by the American government or private interests. The minority which is foreign owned isn't actually primarily held by China either; Japan and many European countries have holdings which are nearly the same size.