China are aggressive in what they believe is 'their' territory, and nothing else. They have no (modern) history of invading or even being involved in other conflicts around the world. Most [large] countries could not boast a similar history.
On the UN security council they veto most aggressive action the US/England/EU press. If further pressed they generally abstain from the vote. Other than territorial disputes where do you get the idea they are 'aggressive' ?
China is out to protect it's interests just like every other nation. The worry is, they are big, and CAN protect their interests. The western super powers are not used to being challenged like this.