@EeveeGoPewPew:
Optimism and Ignorance are the approx. same thing (at least in this situation). Both is based on incomplete knowledge on a topic.
"Nation" is usually used in accordance with government, and if so, then yes, china as a nation knows USA. But that example isn't exactly the best. Lets take America, which is the world of humans, and a much smaller country (to represent fishmen), or even city, one that is VERY distant from the rest of the world (you can fill in the blank here for a country). Both sides will be ignorant of the other side. (humansthink fishmen are just fish, aggresive, etc. We've been shown its not the case, not even close.) (Fishmen think humans are all unpassionate, evil, and does not want coexistence, not even close).
If that were truly the case, then they'd just go to war with each other. In One Piece's scenario, that's what Hodi wants, and what it's almost going to be.
However, Fishman Island is not like China. It's a small country with very powerful warriors compared to the average human. But the WG has even stronger soldiers to beat the fishmen. In addition, Fishman Island would easily be attacked by pirates if a Yonkou didn't protect it. I think Big Mam's empire is more like China, and Fishman Island would be like Thailand. The WG doesn't attack FI because FI is trying to appease the WG. I think this situation would be comparable to the UK appeasing Nazi Germany.
As for the real world situation, neither China nor the USA wants to go to war, because of the potential losses on both sides. The USA is constantly trying to spy on China to get more info about it. China, however, easily gets good economic and social info on the US by simply listening to the news, and a significant quantity of mainland Chinese can understand English. In China, even citizens have difficulty discussing social conflicts because of heavy censorship. It's part of China's defensive strategy to keep its problems under wraps, I believe. The USA, however, is almost completely void of basic understanding of Chinese culture, and constantly assumes things about China based on other 3rd world countries. The USA largely relies on its technology to assume military superiority, and China has been showing rapid technological progress complementary to its economic progress.
From my understanding, China is not as threatening to other nations as the Western world suspects. Europe and North America is too far to have an invasion be economically effective, so that's out of the question. While invasion of the Koreas and Japan seem possible, it's the equivalent of "fixing" something that's not broken. China has a bigger import market with Japan and South Korea is than any other country, and North Korea, while "broken", provides an extra barrier to Western infiltration. In addition, China is already overpopulated and difficult to manage, it doesn't need North Korea to drain its economic resources. Other nations to its south undergoes the same reasoning: not worth invading. There's also the dogmatic rule #1 in Sun Tzu's manual: don't start wars.
Economically, the Chinese have spread to southeast Asia with a myriad of businesses, and perhaps this is the greatest source of threat. In China itself, a racial majority of the Han exists in all provinces of China, including Tibet, Xin Jiang (Uighurstan), and Inner Mongolia. The reason is simply because the coastal provinces, origin of the Han, are overpopulated, under-housed, and extremely polluted. China's currently investing in green housing projects, and entire eco-friendly cities, but it'll be a while before it takes significant effect. I don't know what will happen after eco-cities are completed.
Oops, I forgot that this is a One Piece discussion. The Chinese youth are huge fans of One Piece, btw.