It's not named the Department of War because Congress didn't rename it. Other than that, good on ya.
It is called the Department of War because we live under fascism and Congress no longer matters. All that matters is that everyone calls it the Department of War, and regards it as such, which everyone does.
What you just described is consensus, and framing it as fascism damages the credibility of your stance. There are better arguments to make, which don’t require framing a label update as oppression.