English is a funny language. You can be a competent native speaker and still not grasp anywhere near all the nuances.
Item: I just heard a brief three-minute top-of-the-hour NPR news broadcast. The announcer said that the new U.S. 'security arrangement' with Australia is widely seen as a response to "growing Chinese aggression." My inner antenna switched on: What Chinese aggression? Nothing China has done recently (or not so recently, for that matter) amounts to aggression as I use the word -- that was my reaction.
Then I went to my dictionary. (Dictionaries are not deities, of course, but they're better than nothing.) The first definition of "aggression": "an unprovoked attack or warlike act; specif., the use of armed force by a state in violation of its international obligations" -- yes, that was the sense of the word I had in mind. There is also a second definition: "the practice or habit of being aggressive or quarrelsome" -- that's somewhat looser or broader. Then I went down to the adjective "aggressive"; one of the definitions is: "full of enterprise and initiative; bold and active; pushing." Then there is a little further section which draws fine distinctions among aggressive, militant, assertive, and pushing.
Bottom line? Where I might have said "growing Chinese assertiveness," the NPR guy said "growing Chinese aggression." Is that wrong? Strictly speaking, perhaps not. But I think it's misleading, since "aggression" triggers in most hearers the first sense of the word (unprovoked attack, etc.).
As is well known, China is a rising power in terms of economic and demographic weight (though it also has many problems, which I won't go into here). Rising powers tend to be somewhat "assertive". It's par for the course. That doesn't mean China is going to start a war. Its military is still well behind technologically. Chinese leaders have shown no evidence of exceptional bellicosity. Yes, there are a few possible flash points, but it's nothing to get one's knickers all in a bunch about. Scholars who study Chinese foreign policy closely, like Taylor Fravel of MIT, have shown that China's stance on territorial disputes has been one of compromise more often than not.
Btw, I think having U.S. Marines in northern Australia is not an especially good idea.