expression, godan verb (-su)
open hostilities; take up arms; start a war
Rare, formal, and literary expression. Used in historical or elevated contexts to describe the act of beginning armed conflict.
両国はついに干戈を動かすに至った。
The two countries finally resorted to arms.
From classical Chinese, where 干 (shield) and 戈 (halberd) together represent weapons of war. The phrase literally means 'to move shield and halberd', i.e., to take up arms.