declare war on

Idioms

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.

Example Sentences

Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.

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

Prof Kivutha Kibwana, a law scholar and a former county governor, urged dialogue in his post on X: "The most dangerous thing for a government to do is to declare war on its youth."

From BBC • Jun. 19, 2024

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

The salient policy question was clear: Should the United States declare war on France or seek a diplomatic solution?

From "Founding Brothers: The Revolutionary Generation" by Joseph J. Ellis

Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023