China has become really full of themselves recently.
This attitude of theirs seems to parallel 1930's Imperial Japan, where they believed Asia belonged to them (under the auspices of s "Greater Prosparity Sphere") and like 1930's Imperial Japan, the leaders are military - the Communist Military Commision, which controls the military, answers to the National People's Congress, which has the same members on each board and the chairman of both is the party leader.
So if China seems to be militarily aggressive lately, that's because it is.