Most wars have economic causes and impacts, but that alone does not imperialism make. There are "unprovoked punching down" as well as interventionist components that I don't think describe America's intentions or entries into either World War.
Either way, the argument I'm trying to refute is that me, as a Western Liberal, view any kind of modern war as imperialist, and thus dilute the definition of the term. I think I've demonstrated that while I don't adhere to Lenin's more strict definition, I don't want to use the term lightly, either.
I'm also not trying to make an argument that the USA isn't imperialist, in any strictness of the term. Western Liberals aren't a monolith, my bud.