Doublespeak is used to hide the truth, not to express the truth. The renaming happened in the late 1940s, in a United States that was reluctant to join WWII in the first place, and as the entire world got behind the idea that aggressive war was a violation of the law of nations.
"express the truth"? This is not subjective you know, USA got had more wars in the last 100 years than any other industrialised nation. No matter your political views, the truth is 'department of war'
You're right. It isn't subjective. You're wrong as a matter of numbers, as a matter of legal analysis, and as a matter of history. Stop pushing a political narrative.
https://en.wikipedia.org/wiki/Charter_of_the_United_Nations