declare war on

Idioms  

1. Also, declare war against. Announce one's intent to suppress or eradicate something or someone. For example, The police have declared war on drug dealing in the neighborhood, or Several gangs have declared war against each other. This usage transfers the literal sense of the term, “to state formally one's intention to carry on hostilities against another power,” to a somewhat smaller scale.

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Example Sentences

The attack on the base, as well as similar attacks in the Philippines and Guam, spurred the United States to declare war on Japan.

From Salon • Mar. 19, 2026

Under US law, the president does not have the sole power to formally declare war on another country.

From BBC • Jun. 21, 2025

The attacks prompted Mr. Netanyahu to declare war on the militant group.

From Washington Times • Oct. 7, 2023

But at the same time, the country cannot move forward if Americans declare war on each other and assume communication is impossible.

From Los Angeles Times • Feb. 7, 2022

They asked me if I thought President Wilson would declare war on Austria and I said it was only a matter of days.

From "A Farewell To Arms" by Ernest Hemingway