A declaration of war is a formal act by which one nation goes to war against another. Look up declaration of war in Wiktionary, the free dictionary. Declaration of war may also refer to: "Declaration of War" (song), a song by Hadouken Declaration of War (film), a French film Declaration of War (horse), a racehorse Declaration of War (album), by Rahowa State of War (disambiguation) This disambiguation page lists articles associated with the title Declaration of war.If an internal link led you here, you may wish to change the link to point directly to the intended article.