act of war

American  

noun

1. an act of aggression by a country against another with which it is nominally at peace.

---

act of war British  

noun

1. an aggressive act, usually employing military force, which constitutes an immediate threat to peace

---

Example Sentences

"It was an act of war," Jeffries told NBC's Meet the Press.

From BBC

Allies framed the strikes as a law-enforcement action rather than an act of war.

From Salon

After a ceasefire, Modi vowed that "any attack on Indian soil will be considered as an act of war".

From Barron's

This was nothing less than an invasion, Khrushchev charged, an act of war.

From Literature

A blockade, like an air strike, was an act of war.

From Literature