You're right about reason #1. And you've probably heard about strong contenders for #2 and #3.

There's a famous quote attributed to the Italian military commander Gian Giacomo Trivulzio in 1499.

When asked by King Louis XII of France what preparations were needed to invade the Duchy of Milan, Trivulzio responded: "To carry out war, three things are necessary: money, money, and yet more money."