You stated..... China is highly expansionist, it wants land - mainly because it wants resources.
I have not studied much about the Resources of China...but why is it so necessary for them to do so......I speak of water and other natural resources....
China has basically 3 natural resources:
1. People (1.4 billion and counting)
2. Land (about as big an area as the US)
3. Coal (low grade, but lots of it)
They do not have much timber reserves. Very little petroleum or metals. Very little clean water (all their rivers are like the Mississippi - slow and muddy but with extra polluted).
To continue growing, they either keep importing, or find new domestic sources of these items. Thus the push to the Spratley Islands (petroleum) and the focus on Siberia (cleaner coal, petroleum, wood, land).