Declarations of War end with a Peace Treaty.
In Iraq, we ended a Cease Fire, and used UN Resolution violations.
These days we dont make declarations of war because we want everything to be a "unified effort" among several countries, and "unilateral" strikes are considered as bad thing these days.
I'm looking at Wikipedia's article titled Declaration of war by the United States.
It contains two lists - "Formal declarations of war" and "Military engagements authorized by Congress".
According to the article, Congress began the practice of authorizing the use of military force without a formal declaration of war in 1798.