declare war

declare war (third-person singular simple present declares war, present participle declaring war, simple past and past participle declared war)

1. (of a governmental authority) To make a formal pronouncement, or sign a legal document, that initiates a state of war between one nation and another, usually before hostilities begin.
   • 2007, Carlos Ramirez-Faria, Concise Encyclopaedia of World History:

     Germany declared war on France, who reciprocated, on August 3 [1939], and England declared war on Germany on August 4, when Belgium was already under invasion.

2. To announce one's intention to fiercely combat or eradicate something.

   The governor declared war on poverty.

   • 2011, Henry Hampton, ‎Steve Fayer, Voices of Freedom: An Oral History of the Civil Rights Movement:

     Leo Lillard, a Nashville native attending Tennessee State University, had become involved in the sit-ins as soon as they started. It was no longer just the students, it was clear that the town had declared war on racism.