The United States had a plan that would have killed one third of all people on the planet (1 billion of the 3 billion alive in the early 1960s).

Source: "The Doomsday Machine: Confessions of a Nuclear War Planner" by Daniel Ellsberg

Militaries do all kinds of planning - doesn't mean that anyone has the intention of actually executing them.

e.g. The UK did war planning of invading Eastern Europe after WW2:

https://en.wikipedia.org/wiki/Operation_Unthinkable

Obviously, the conclusion of this planning was that it was a bad idea...

Before WW2 the United States had a plan on how to fight the British Empire:

https://en.wikipedia.org/wiki/War_Plan_Red

Around the same time the Canadians had plans for attacking the USA:

https://en.wikipedia.org/wiki/Defence_Scheme_No._1