> However, that passage provides no specific format for what form legislation must have in order to be considered a "declaration of war" nor does the Constitution itself use this term.

Furthermore, there's no doubt that the U.S. can be at war without an official declaration by Congress: those instances when another country formally declares war on the U.S. first.

For example, the U.S. was officially at war with Japan from 7-8 December 1941, for a few hours with Germany and Italy on 11 December following their declaration of war against the U.S., and from 13 December 1941 to 6 June 1942 against Bulgaria.

https://en.wikipedia.org/wiki/United_States_declaration_of_w...

http://en.wikipedia.org/wiki/United_States_declaration_of_wa...

http://en.wikipedia.org/wiki/United_States_declaration_of_wa...

The American Civil War doesn't count either, then?

It would be rare to see any civil war count as anything other than infighting.

The American Civil War was considered an insurrection by the victor (Lincoln), thus that's what it'll go down as in the history books.

So it's an illegal war. Still a war.

No, Congress explicitly authorized all the conflicts the article is talking about.