Here is a simple idea. There are no evil nations and there are no good nations. All nations will maximize its interests if their circumstances allow it. All nations will be maximally aggressive if their circumstances allow expansion. All nations will be maximally defensive if their circumstances show huge risk of reduction.
US can be maximally aggressive in its foreign policy cause it has no internal problems, huge wealth, no internal regions to pacify, no near neighbors that are not US client states. it has a strong central government ruled by people from single ethnic/European culture. New immigrants also get assimilated into this culture and do not cause separatism problems which could direct national energy to other areas.
China in the past did not expand beyond "China Proper" for thousands of years because its surrounded by regions that are not that productive, deserts, mountains. It is surrounded by regions that are very remote and hard to go to, thus much harder to control from the center, finally just controlling the core areas of China was already bigger than Europe and probably too much to control, thus existing government could not handle bigger land and population.
But most dynasties had phases when they had less problems and could expand much more from their core. Thus, Tang dynasty had huge land in the west for some time but song did not. ming dynasty also could not expand much. But Qing dynasty achieved strong internal cohesion and ability to expand. Which it did.
So, how aggressive will modern China be? As much its power, national cohesion and outside environment allow it.
Right now China's main focus is economic and technological parity with the west. They have rightfully identified that this world is dominated by a group of europeans and european settled countries who have colonized the world for 200 years and have been the dominant force even after decolonization.
So, their main focus is to bridge that gap and become equal to the so called europeans/whites. They must achieve equal GDP per capita, which means around 45K. They must achieve technological parity.
Another goal for China is to end internal threats. Thus, end separatism, end ethnic diversity to create a single Chinese cultural identity shared by all.
Only after achieving these two goals can they really focus on foreign policy goals. Their biggest foreign policy goal is to make China secure by ending the power of other powerful nations and groups. The biggest such group is white-europeans/euro settlers and their alliance.
Thus, their biggest goal next which will make them secure is to end the dominance of the europeans/euro settled countries. Which means kicking them out of East Asia first. China needs to achieve absolute military dominance in its backyard so that Europeans do not dare to fight China in its own backyard thus threatening China's economic and territorial well-being.
Forcing the white/european settled countries to focus on their own backyard instead of interfering in China's backyard can be one strategy as well. Which means China will have to take their influence and military to the backyard of US and Europe. They must forge strong relationship that live in those areas but under the thumb of europeans and Euro-settled countries. Thus, Mexico, Brazil could become strong allies in the distant future. Muslim countries in the Middle East and Russia are big threats near Europe as well and they will become natural allies of China as well.
Finally, once they achieve that goal of forcing those europeans to focus on their own backyard, then their next goal will be achieve complete dominance of its own baclyard. Thus, no more Japan or Korea being client states of US. They must be client state of China. They must consider China to be the source of culture and soft power. Thus, China must do a regime change in those countries, and if that is not enough. Then do a complete take over. South East Asia should be next target for Chinese dominance.
China must also focus on South Asia and Russia and end the threat of those countries too. Which means breaking India and Russia into small pieces if possible. If not possible, then do a regime change to bring governments that are friendly to China. If not then they can offer them to ally with China. Or they can force them to focus on their internal problems, thus fomenting rivalry with say Pakistan or even internal separatism.
Finally, in order to make China completely secure, they must break the European-euro-settled alliance. Make those countries start fighting each other. Even break countries into pieces. Such as breaking US and europe.
As you can see, there are many many huge tasks that China must do to secure itself. Whether China can do them depends on ability of the Chinese state, Chinese people, the inability of other states, internal problems of others states as well.
Its a constant struggle called geopolitics. How many of these goals will China be able to achieve? We don't know. But we can make guesses based on how the world is right now.
One thing I am certain, China will most certainly achieve the first goal which is China becoming as Rich as Europe and Japan. Which means China will also achieve the biggest GDP, 3-4 times bigger than US, biggest military budget, best technological military. What happens after that? I don't know. But my gut feeling says, the next few centuries will be dominated by China gaining power influence and slowly eroding and degrading the west.
China will do to the west, what they did to China. A century of Humiliation.
