Not to mention hijacking other accounts that would plausibly say things along the same lines as "proof" that the statement is real.
Even after dozens of high profile accounts were hacked many were still commenting that they didn't think it was possible for it to be a twitter vulnerability, but rather individual accounts being compromised or a 3rd party. If you only tweeted plausible things about war and corroborated it from multiple accounts at the same time you can reinforce things pretty easily.
Considering that they got Obama's account as well, you could very well create a narrative and counter narrative using the POTUS and ex-POTUS accounts. For the sake of fiction, you could have Obama tweet that he is, indeed, taking over, and arresting Trump. Maybe not war, but it could exacerbate the lack of trust across political divides.
What could be dangerous about it is that CNNFOX et al would copy-paste the story without fact checking, inflate it, and make as much money from it as they can.
Even after dozens of high profile accounts were hacked many were still commenting that they didn't think it was possible for it to be a twitter vulnerability, but rather individual accounts being compromised or a 3rd party. If you only tweeted plausible things about war and corroborated it from multiple accounts at the same time you can reinforce things pretty easily.