Is there any nation in the world today that has not upset others with their territorial claims? Don't think for a moment that the United States of America hasn't. Turn the clock back and you'll find the USA - even before it became fully established as the USA - was pushing the Mexicans out of of California and New Mexico, the Canadians up a few degrees of latitude, and, after World War it's victorious war over the Spanish, grabbing the Phillipines.
The USA also made sure that it had control of many strategically placed island, such as Wake, Midway and others which it hold to this day. Then there is their foothold in Cuba. Gauntamino Bay is not in the United States but try telling the Yank military that!
Of course, the Yanks got off to a late start. When I was a kid 'good old blighty' (Great Britain) had an emplire on which the sun never set.
I'm not condoning China for any expansionistic ambitions. We know how they just marched into Tibet and claimed it as their own. But don't get the idea China is any more beligerent than many other nations. Take a look at what's going on around the Black Sea at this very time.
Sure it would be good if the United Nations could really do anything regarding the ambitions of the major powers. It can't. Because it is an 'organization of nations' in a time in history when national boundaries should be redundant.