Dalswyn: (sorry for the late answer)
Yeah, the so-called "century of humiliation". While there is no denying that China was a victim of what you call "Western and Japanese imperialism" (sometimes gruesomely so) and that these aggressions left deep scars, your university course seems to have painted a rosier image of China than reality.
Things certainly
did not mellow out under Deng Xiaoping. After all, he was the supreme leader during the Tiananmen square bloodbath. The "century of humiliation" became a systematic tool of propaganda (and school curricula) as a reaction to the massacre. Why? Because the CCP's leadership saw what was brewing in the Soviet Union and its satellites, and they began to shit their pants at the idea of people demanding things of the government and threatening to topple it. Today, they would like to have the chinese people believe that nothing happened there and then, but at the time, the population was shocked at the army killing peaceful protesters.
Chinese protesters. Hence the recourse to that time-honored practice of blaming the foreigners for everything that went wrong in living memory. THAT is what prompted the CCP to ramp up the rhetorics of China having been wronged. By the way, the rejection of confucian dogma was quietly reversed when it became convenient (see Confucius Prize, Confucius Institutes, etc...)
Secondly, it should never be forgotten that China sees itself as
中国: the Middle kingdom. For millennia, they considered themselves to be the literal center of the world, surrounded by "barbarians" (if you've never heard of Empress Suiko's letter to the chinese emperor, do yourself a favor and look it up: it is both hilarious and enlightening). For many centuries, China took tributes from other countries as a mark of submission. To refuse to send an adequate and timely tribute was, at best, to be unable to trade with China (does it sound familiar? Wink wink nudge nudge), at worst to expose yourself to a military invasion.
Thirdly, to hell with the myth of the peaceful China without a colonial empire. What is happening today in Xinjiang - a meticulous, cold-blooded genocide on an industrial scale) rightly calls to mind the Shoah, but China's no beginner. Systematic attempt to destroy a foreign culture? Check (eg. Vietnam in the 15th century). State-led, years-long ethnic cleansing? Check (eg. the Dzungar people in the 17th century).
I won't pretend to be an expert on China. Being a neighbour, you probably know more about the local history than me.
I have no illusion that China won't be a bully if they are given free reign, its just how people are. In a way, its good that all the major players have nukes (it imposes a certain degree of respect), though as a software developer, I do worry quite a bit about cyber-warfare (my biggest personal worry about China honestly).
I do know about the "Middle Kingdom" mentality (and the dominance strategy by trade), though to be fair, being in a large dominant country brings out that kind of mentality in some. You'll find some people that are like that in the US too (in movies of course, but also in the way some people talk).
But yes, China, as a dictatorship, can presently afford to be more uncaring about human rights (part of the reasons I would not go visit China). However, I would be remiss not to mention that while they have at best a tenuous grip on power, extremists south of the border hold enough influence to be pretty scary and we have some of those in our own backyard too (Proud Boys, Combat 18, Blood & Honor, etc). Also, after 9/11, there was a palpable atmosphere of Islamophobia that unsettled me quite a bit (though I think its better now).
Its not very difficult to imagine how things could feasibly go very bad, no matter where you are.