In every bussines you have a cost to produce something and a revenue. You can invest in missiles and then steal resources from other nations. But how did you buy those missiles? With fiat currency.
The cost to produce fiat currency and bank credit is cero. And they get real wealth as collateral that they can keep squeezing the credit supply: tax revenue, homes, securities. The return over investment is infinite. This is without a doubt the most profitable bussines on earth.
Printing a $100 dollar bill cost 14 cents according to the Bureau of Engraving and Printing (BEP). Thats $99,86 in profits from the face value purchasing power of a $100 dollar bill.
Now think about printing digital currency or bank credit. The cost is cero. Infinite returns. War may be profitable as well, but making everyone believe you fake fiat currency is money, is defiantly the most profitable business on earth.