"Why does China think we will attack them??"
Because we might. Imagine a world where china was wiped off the map. Manufacturing jobs for everyone and cheap oil. It has to look very attractive to 10% of the population of the US. Ok, extermination of over a billion people has its drawbacks but the people of the US have gotten used to the good life and being top dog in the world. Exterminating china would solve a lot of problems.
I will say that 90% of the US is opposed to this because they are decent people, but 10% of the US would kill their mother for cheap gas, lots of money and returning the US to top dog status. Hell, we have 20,000 people killing US citizens every year for a lot less than that.
But enough about the Democratic Party...