expression, godan verb (-su)
to start; to begin; to kick off
Idiomatic expression literally meaning 'to cut and drop the curtain', used for the start of a dramatic event, war, or new phase. Often carries a theatrical or momentous nuance.
See also: 幕を切る
新社長の就任で、改革の幕を切って落とした。
With the new president's appointment, they kicked off the reforms.
その事件が戦争の幕を切って落とすことになった。
That incident ended up starting the war.