Google 9 dash line
Google belt and road initiative
People are upset that China isn't honoring their agreement and are dismantling the democratic system and free speech HK is enjoying now, these are universal human rights. Rather than China learning from what made HK so prosperous, as they were for a while, the new leadership is heading back towards the old Maoism policies that lead to the massive starvation and famine and lost generation. Any foreigner living in China is treated terribly, can't do basic things, can't become a citizen, and is constantly checked in on or followed by police. They keep all their citizens in a social credit system, they send religious minorities to labor and reeducation camps, harvest organs from them, etc. Not surprising from a country that teaches about and speaks of Hitler in a positive light, you can't really criticize Hitler without criticizing one's own self and past policies. The US at least admits the things it has done that were anything close to that were wrong as they oppose our own values.
To say nothing of Taiwan, an independent country with its own government and system that China still claims is part of their domain, rather than simply accept reality. It has become imperialistically aggressive towards Taiwan and demands airlines and hotels, media, sporting events etc not show the Taiwanese flag, refer to it by its name, or do anything that indicates the reality that exists now, which is that Taiwan is its own separate country and an example of what would have happened if the democracy had taken root in China, where you'd still have free practice of religion and Chinese values, a strong economy, good health care system, free access to information, etc. If you want an example of Chinese imperialism, look no further than Taiwan, the only reason they haven't invaded Taiwan is because they know they can't without serious consequences.
The old wars were at least excused as staving off invading forces that were seeking eliminate democracy. South Korea is its own country now, they have democracy, look at the DPRK versus SK, we were literally fighting evil and SK is better off for it. Same for the other countries. We're pretty crappy at imperialism if that's the goal since none of those countries are part of any kind of empire and we barely have any influence over them. Thankfully Vietnam didn't end up like DPRK and adopted capitalism at least or a much less dictatorial version of communism.
At least in the US, you're allowed to read about the ills of imperialism and criticism of past and current government actions. In China, you can't even compare the leader to a cartoon character without serious consequences. If the government is doing something wrong, you as a citizen wouldn't know about it and wouldn't be allowed to speak publicly about it, much less organize a protest against it.