The last time the US officially declared war was for?

In 1941, at the request of President Roosevelt.

Soon after that the post office issued a "Win the war stamp", and other stamps supporting the war effort.

Since then, even though we have had wars, no similar stamps have been issued and I wondered why for awhile-- and then it dawned on me-- we really never tried to win any of the wars after WW II- there were no clear objectives, Congress did not declare war and the nation as a whole was not involved in the war effort. Our soldier swere dying, but it was business as usual for most Americans- not even a tax to pay for our current war.