Raise Army - In a time of need, you can raise volunteers for an army. The number is equal to 2^Fighter Level. So a first level fighter can rally a couple friends, a 6th level fighter could raise a company (64 people), a 10th level could raise a regiment (1000 people), a 15th level could raise an army (30,000), and a 20th level fighter could mobilize an entire population (2 million).
Surprisingly enough, the numbers work. I would say that they break down at high level, but this by high level, numbers are supposed to be awesome. At 20th level, you're the king anyway.
I assume that you raise lots of level 1 warriors. If you assume CR, then you can instead buy more expensive forces. If you are smart, you hire more fighters to raise more troops. (That's called the feudal system.) You can also use it to get elite troops, monsters, etc. That way, you don't really raise two million people, you just raise an fricking super-elite army.