What does "declaration of war" mean?

A formal announcement by a country or other body with military capability that it is in a state of war with another such entity.

Declaration of war

Common synonyms include: challenge, declaration, declare war, defiance, hostility, proclamation of war.

noun

noun ·Rare ·Advanced level

Noun

1
A formal announcement by a country or other body with military capability that it is in a state of war with another such entity.
"Make no mistake, the sway of the railways' mandate in the middle of the 19th century was, in some quarters, a declaration of war on the old."

"Make no mistake, the sway of the railways' mandate in the middle of the 19th century was, in some quarters, a declaration of war on the old."