There's a theory called "Thucydides Trap" which refers to when a rising power causes fear in an established power which escalates toward war. In this case its America and China. Does it have to lead to war? No. But it often does.
The problem is nobody really knows just how good or how bad China's economy is in besides China. The problem is if a war between nuclear powers happens, does it go nuclear? We've avoided this situation because basically every nuclear power fights proxy wars now. Its been done since the Cold War. Syria won't cause a World War, because its just a proxy war over spheres of influence. Territorial wars aren't really fought by nuclear powers because that's how you drag everyone in. You've got trade wars, cyber warfare, espionage. They've basically figured out ways to stay in perpetual competition without pressing the button.
The main problems are two-fold: DPRK and the South China Sea. Its only a matter of time before the DPRK collapses in on itself or there's a verge of a coup happening. Or that they just lose their minds and launch an actual nuke. We've allegedly infiltrated their infrastructure completely, but the US now wants the situation resolved. People are tired of their shit. If China goes to bat for them (I admit this is unlikely as a DPRK with ICBMs won't be tolerated by pretty much anybody) and someone gets nuked in the end, people could be pissed off enough to blame China for it. That escalates into trade wars and outright conflict over the South China Sea.
If the DPRK is resolved, you still have the South China Sea. Which pretty much nobody knows how to handle. One the one hand, nobody wants to go to war over it. On the other, nobody is really comfortable with China controlling such an important trading route. Its really easy for a misunderstanding to happen, but I doubt it. China is already paranoid about being surrounded by so many US Allies. Maybe they can be bought off by saying 'Kill the DPRK and you can keep the shitty Korea as a buffer'.