President Koichi appointed Viet as the next Secretary of State, but he refused.
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means cut off. What happens when you do the action of cutting someone off? You're going to refuse them of whatever it is they want.
By trying to refuse this person, you're going to start a 事 war (a war of actions). They will do one war-like action, then you will do a war-like action until it escalates into a 事 war (ことわる).