War is one thing that no society should engage themselves into as its effect is devastating and unforgettable upon generations.
Not devastating to bankers however - quite the opposite.
You see, after a war, the countries involved get loans from banks to improve their economy (money which they can create from thin air as an entry in the database because they are allowed to). They have to pay regular interest fees to those banks, and that makes the owners of those banks stinking rich. So they actually profit from the outcome of a war, either direction it goes - as long as their own country is not invaded.
The United States, after the end of World War II, became a powerful country precisely because its territory was not affected by hostilities. At the same time, the industry and agriculture of many potential US competitors were completely destroyed by the war.
See the paragraph above. It's because they loaned money to the Allies and Axis countries.