I've got it. So, Klingons, and prelude to war with same.
Kirk and Marcus are dating. Marcus is secretly pregnant. Marcus gets captured by Klingons and is killed as a demonstration of resolve.
"You Klingon bastards you killed my unborn son!"
But seriously, Klingons. As others have said, the whole Organian intervention will probably not happen this time. I suspect had both parties not landed on Organia it never would have.