Before we get to foreign exchanges
Finance 101: It's a zero-sum game, for some people to win others have to lose.
There are 4 rungs:
-The lowest rung in this game is guessing what's going to happen and then gambling with investment, this is not sensible, don't do it this is the looser-rung.
-The next rung is having insider information about what is going to happen so that you know what you can invest in with a guaranteed return.
-The rung above that is having the ability to affect the world in a way to make your investments give you returns.
-The top rung is having control over institutions so that you can rig the game in your favor.
Foreign exchanges are affected allot by foreign policy of countries, if you can get insider information about decisions in that field before it's made public, you can sensibly predict it and make some money off it. If you're the one making foreign policy decisions that's also a way. Controlling something like a central bank, that's probably the best position.