Department of Defense was the actual lie, the newspeak term. They were not really defending anything, they were using military power globally for pursuing economic interests. However, it was easy to convince people that the whole endeavor was a good thing, because defending your country against the baddies is good, and you should support anyone doing that (otherwise you'd be a traitor!). Thank you for your service (defending us).

On the other hand, the term Department of War is hard to sell, because most people don't want to participate in a war or support someone who wants to start one. Thank you for your service... invading other countries? killing and raping innocents? ransacking resources?

This is an irrelevant detail, but if I'd read the title "Department of Defense vs. Meta", I'd first think Meta is leaking confidential info to other countries. However, if I'd read "Department of War vs. Meta", I'd think Meta doesn't want to promote an unnecessary war.