The definition of Inflation is actually inflation of the money supply. With more money in the system (Supply is more), hence the value of the money is less as the goods and services in the system remain static. So the actual result of the inflation is increased prices. So now people actually use the result of inflation as the definition for inflation (i.e prices going up is referred to as inflation, or the CPI (consumer price index) goes up or down is called inflation) which is incorrect. The inflation is there when the money is printed, the prices will go up later as the money makes its way through the system, so this is actually mathematical.
So the next question is what causes the money supply to be expanded. Well that is debt, government debt and close friends of govt that get bailed out (such as the banks with QE in the US). So in the long run foreign exchange rates will be based on fiscal responsibility of countries and their debt levels (both public and private that would get bailouts).
The US Dollar is the reserve currency of the world, and oil is always purchased with USDs, hence the USD is also referred to as the petrodollar. This creates a demand for USDs for any country that wants oil (all of them), as they need to purchase USDs to purchase oil. Things are changing as more countries are looking to purchase oil in their own currency and when/if this happens, the demand for USDs will drop dramatically and all that inflation (expansion of the money supply) will go after all other goods in the US and prices will increase substantially with US foreign exchange rates not doing well. Obviously this would not make the US happy.
This is as short a possible answer that can be given to this question.