It depends on how you want to measure a nation's wealth! It's probably easier to measure GDP and things like that as opposed to societal happiness and human rights etc etc, things that are harder to quantify.
As it currently stands China is set to take over the USA in the next few years as the world's Economic Number 1. But I wouldn't say that means decline for the rest of us in the west.
But many smaller nations are desperate to do business with this new Chinese giant. As the stock markets build, fluctuations in the China market will have increasing influence on us all.
I guess the world has historically had empire building as its modus operandi...The Roman Empire, The British Empire, The American Empire arguably....now we've got the Chinese empire to think about.