Thats kind of a big topic. I'll take two tiny little subtopics.

The "best" greediest smartest whatever-est minds over centuries of human history have never found a way to keep a global reserve currency for longer than a century or so. There's a famous chart of ranges of time where the Spanish had the worlds reserve currency or the English or whatever. And the US dollar is gettin kinda old as global reserve currency. This is very much like the graphs of devastating earthquakes in CA, you can't predict the day and time CA will be pretty well flattened, but pretty much everyone in SFO does die and every building gets flattened "about once a century". Changing reserve currencies happens about the same way. I'd be an idiot to claim it'll happen tomorrow or next year, yet its also a near 100% certainty looking at history that my grandkid will grow up under a new reserve currency. China is getting ready to economically collapse and have their own great depression looking to be about 10x worse than ours, until they have another revolution, so not them, they'll be too busy starving and killing each other. My guess is after the .eu and the euro collapse, the German Mark will be re-issued and become the new global reserve currency that is used for all world trade. Or some game in name only, where the .de totally take over .eu, rather than the current just mostly having control of .eu, and what we will call a euro will really be a German Mark. I'm thinking 5% odds its bitcoin or a derivative digital currency, maybe 55% odds its German Mark or synonym, and the remainder is an unclear mix of a new S.U. currency, or maybe Africa will get itself together (gonna happen sooner or later unless someone stops them). Or the century old battle of hemispheres has the south rising, perhaps some kind of Pan South American euro-like "thing" will arise. At least most of them speak more or less the same language. So we're getting a new reserve currency "within a generation" and it definitely isn't going to be the dollar. This isn't the end of the world, London is still a nice place to visit, but it does mean certain changes will occur.

Another topic worth discussion is the end of cheap oil, which has more or less already happened (unless you're getting gallons of gas for 90 cents in the USA?). All the fields worldwide are in decline and discovery and production per dollar invested is in permanent long term decline. So all business models oriented around pumping oil/natgas out of the ground are on borrowed time. Generally any good news as a counterexample is innumerate, either no understanding of quantities (so the lifetime production of a TDP plant is about 5 minutes of USA consumption, awesome) or the standard manipulation of statistics (so production at one well went up 10% month on month last month therefore if you extend that into infinity we're going to have worldwide oil prices of 10 cents/barrel) or just technoutopia, usually horribly out of date "Hey guys, I just heard about this new thing, ethanol plant, and its going to save the world" LOL thats already crashed and burned.

There is probably some connection in that the USA .mil will probably hold things together enough to keep the $ as the reserve currency as long as oil tankers import oil into the USA. Once that stops, and it'll stop soon enough on existing trends, the motivation to maintain global conomic control will likely evaporate and thats when we'll get a new global reserve trading currency. Watch for S.A. oil exports to irreversibly start to fall and then expect some financial chaos. Everyone else, .mx, UK north sea, all in decline already (LOL Britain has gone from being a natgas exporter to being an importer in just the last couple years)

The middle class is made of natgas, which is interesting. You turn natgas into AN fertilizer and turn that into corn and turn corn syrup into lots of middle class biomass. Also you turn natgas into plastic consumer garbage and that gives the middle class something to advertise, make, ship, retail, purchase, use, aspire to... Without natgas that whole segment of society simply evaporates away. What kind of fish you got when you take the water out of the fish tank?