It’s quite telling that the examples you have to bring up of the US annexing territory are from over a century ago, before we had developed modern concepts of international law. We’re supposed to be past the era of annexation by force.
The area that China is annexing is not empty ocean, it’s a set of islands that belong to other nations, like the Philippines. Those are not theirs to take, and it’s a breach of international law, but their military power and UNSC veto means they can get away with it.
And, no, the conflict is not because of US activity. It’s because China, as it quite openly states in various forms including its doctrines, believes it has the right to regional hegemony over neighbouring countries. They, in turn, obviously don’t want that, so they’ve invited the US in as an ally. None of those are ‘aggressor’ moves toward China, because even the largest US military facilities in the area only have sufficient forces for defensive actions, not for an attack on mainland China.
The US didn’t invade Korea, it was part of a United Nations force protecting South Korea from attack by the north. It invaded Japan after being attacked first at Pearl Harbor. It was invited into South Vietnam, at the time under attack from North Vietnam. Laos I’ll give you, that was illegal and unacceptable. The US has never invaded China, it had a post-war force at the request of the then-government to disarm and repatriate the remainder of the Imperial Japanese Army from Manchuria. Similarly, it liberated the Philippines from the Japanese and immediately restored its pre-war democratic government. That’s not an ‘invasion’ as you cast it.
Of course of this is to say the US has always done good or is perfect. Far from it. But your whataboutism and insistence that China has done no wrong is ridiculous.
In the past two decades alone China has been in border disputes and land grabs with nearly all its neighbours, encroaching on territory in India, Bhutan, and the South China Sea. This should not be considered acceptable either.