Just from various musings and investments, my understanding is the world was once under one currency, precious metals, especially gold. It was the the way in which countries amassed wealth.
As wars broke out in various regions, over time, that wealth started to gather more in some countries and left defeated countries scrambling for other means of trading with. This trend kept going until almost all mined precious metal, at the time, was distributed between just a few major countries or civilizations.
In turn, countries without, evolved & devised notes (loans+IOUs=dollars) as a way to support themselves during times of hardship and wars. Which inturn lead to what we have today. Now, I've condensed the process greatly in this explanation.
Inflation now happens when countries start borrowing more, year over year, than they can afford to pay back, wether with paper, product and/or precious metals/materials. Once this happens then their own paper (IOUs) become a liabillity to trading, hence their credit worthiness goes down, and it takes that much more of their paper to trade with.
As I stated before, this is a condensed version of how it all works. And my understanding of the situation as a whole.
Edit: Just for further clarification. That's why the English pound holds the highest value, because it's based on gold and always has. The US dollar at one time was based on gold, but after the breakaway from England, they found other means, oil, which was thought at the time to be of long lasting (resource-wise) infinite way to back trading.
For the US, the inevitable happened. Oil was discovered to be finite, and with the ensuing conditions, wars and all, are now in a pickle to find another way of backing the dollar. Wether that be through making products or whatnot. Most other countries are in a similar dilema, trying to find a way to back their currency for trade.