There are two types of empire, there is the uniting of a group of peoples with no common ethnic background into a single unified entity by force, and that's an empire. China today is that kind of empire, the USSR was that kind of empire a few decades ago. The US is not that kind of empire. Many people misidentify the US as that type of empire, but the differences are huge and practical.
However, there are trade empires or federations, that unite such peoples for the purpose of trade and commerce. The US is indeed the leader of a trade empire that stretches to every part of the world. In a trade empire, differences between peoples are slowly erased as they move freely between nations for the purpose of trade, and that's exactly why we have much of the unrest in the MidEast, they do a lot of trade with the US/Europe/Japan and this causes their culture to "want" to converge toward that of their trading partners. Since this convergence will represent a major power shift away from their established church, this is resisted by traditionalists, often violently.
To be perfectly clear, western culture is not being forced on anyone, you are simply able to make better business deals and make more money if you are able to understand the people you deal with. You encourage your daughters to dress in their styles when they meet these people, you learn their languages, you visit their countries, and you will become "westernized". And you've got a lot of influence because you are now rich. And that's what the world is doing and that's a large part of the reason why the US is the hated one now, because we are seen as the core of this change in the world.
As for Ferguson's thesis, the wealth does get redistributed eventually, by force if necessary. China had periodic revolts in the provinces, and during those revolts the peasants would rush into the palaces and hunt for gold or silver or anything of worth. This they would later use to buy land or set up in business. And that started the cycle over - Pearl Buck wrote of that entire cycle in "The Good Earth". This happens everywhere, somehow, whether Robin Hood sets up in Sherwood Forest or you have buccaneers working for the queen, the wealth does not and cannot be placed into a cave and guarded, this has never worked in history and it cannot work now. Ali Baba's cave is a myth, but even in the myth, the poor man got the gold in the end.
Because of interest, wealth tends to flow uphill. Every society has tried to prevent this from happening since the invention of money, I can quote the Old Testament on usury if you'd like. There is no successful society that I know of where the wealth does not get redistributed or destroyed in some manner over a full sacelum (many unsuccessful ones, but that's another issue) and we will either break down the ultra wealthy or destroy their wealth or we will fall in this cycle and another society will take over in our place, doubtless with a different currency which will make the point of "what I was worth in dollars" kind of moot.
A new class of wealthy will emerge, and the cycle will start over. And this time it may well be short circuited by the coming singularity, but we've quite a bit of time to get through before that fully hits, more than enough time to see things fall apart and come together again.
This just popped up, if you like stories of overzealous government, this one's a winner. And don't leave the country with an antique wooden guitar.
http://online.wsj.com/article/SB1000142 ... stpop_read
Or search on "Guitar Frets: Environmental Enforcement Leaves Musicians in Fear".