The Federalist Adams Administration was Pro-British, but America had a number of outstanding complaints against the British, including
impressment of Americans into the Royal Navy, the lingering border adjustment between the USA and North Carolina, and the status of Prince Rupert's Land, and rescinding of the contentious fishing rights off the North American Coast. All of these the British were willing to cede to the Americans if they would support the war against France, as well as reaffirming the Mississippi as free for navigation and the right of Deposit in New Orleans should they prove victorious. The Anglo-American Convention of 1803 settled these issues, and Adams went to Congress for a declaration of war.
The Americans never joined the Coalition officially, and in fact due to the Washintonian admonishment to avoid entanglement in European wars as well as lingering affection for France among the Democratic-Republicans and the Quebeckers, though this had been eroded by some of the high-handed actions of the French on the high seas. Thus not only was the vote for the declaration of war one of the closest in American history, it was also one of the oddest due to the political sensibilities of the time. Thus did the United States not declare the War of 1804 on France, nor commit to battle anywhere outside the continent, but instead declared it upon "Napoleon in North America".
The British rapidly seized control of New Orleans and Louisiana south of latitude 36-30, while American forces took control of the Mississippi north of there. In addition, American forces took the small islands of
St. Pierre and Miquelon. In the ensuing peace, France ceded these lands to the United States, as well as releasing their own fishing rights off the North American coast. Britian would hold the vital port of New Orleans as well as the Louisiana region below 36-30.