Turns out Harry Truman had a bit of Machiavelli in him. The news article below indicates that it would be a good idea to let Germany and Russia fight it out. And of course, help the side that was losing so that they destroyed each other thoroughly.
In military parlance this is known as the “Bait and Bleed” strategy.
This is not exactly the most humanitarian thing to do. Nor is it justified from a philosophical perspective.
But Sun Tzu would love it.