China:2.5 carriers isn't going to be much of a challenge to 43 carriers.
a) Thinks in the long run.. gotta start somewhere to train a deep blue see navy. So they start now. Countries near China have no real navy (even India's is no where near as large.) And China now contest who owns the seas near their border. That can start wars.
b) With over a billion people to feed (and being communist) have a very fragile system that can fail. And if it fails there will be MUCH internal trouble. Thus need for external distractions. That can start wars.
c) China just made their leader, Xi, in 2018, abolished 'term limits' thus he is de-facto RULER FOR LIFE. I.E. dictator. Dictators can start wars easily.
d) China is an enemy of India (also over a billion people) and have constant small border wars... these wars can escalate (and the USA is allied with India.) Another way a war can start.
e) China has massive environmental problems. If it gets out of hand... wars can start.
f) China needs more exports lease there become massive unemployment. Due to China's one child policy they now have millions of more males than females. This can disrupt the social fabric.... and wars start that way to.
These and more reasons can bring about an unexpected war. Like most wars the leaders 'think' they can win. Sometimes they do, but most times they really don't.