Has the United Kingdom ever declared war on the United States? Was war declared against the colonies in 1776 or later? What about 1812? Did parliament or the king ever admit that a state of war exists between the United States and the United Kingdom?
In 1775, George III declared that his colonies were “in rebellion”, which is considered tantamount to a declaration of war. However, one does not officially “declare war” on one’s own colonies, partly because hey, it’s family, and partly because that would grant them the symbolic status of an actual “nation”, which was not what he had in mind.
http://www.britannia.com/history/docs/procreb.html
In 1812, the United States declared war on Britain.
http://www.state.gov/r/pa/ho/time/jd/16314.htm
Relationships were a bit sketchy long before the War of 1812 actually got started. The major issue was the British raiding American shipping and impressing American sailors into the British Navy. The British didn’t declare war because they were trying to maintain the pretense that these actions had some sort of legitimacy, so there was no official conflict until the United States declared war.