Title: War of 1812
Content:  The War of 1812 (18 June 1812 – 17 February 1815) was a conflict between the United States of America and its indigenous allies, versus Great Britain and its allies in British North America, with Spain providing limited support in the south-east. The United States declared war on Britain on 18 June 1812 and although peace terms were agreed in the December 1814 Treaty of Ghent, it did not officially end until ratified by Congress on 17 February 1815. Tensions originated in differences over territorial expansion in North America and the Royal Navy blockade of American trade with France during the Napoleonic Wars, exacerbated by the impressment of 
Title: Results of the War of 1812
Content:  The results of the War of 1812, which was fought between the United Kingdom and the United States from 1812 to 1815, included no immediate boundary changes. The main result of the War of 1812 has been two centuries of peace between both countries. All of the causes for the war had disappeared with the end of the Napoleonic Wars between Britain and France. The destruction of the power of two major pre-war pro-British groups in the United States (the organized Native American confederacies and the Federalist Party) opened an "Era of Good Feelings," which reduced partisanship and an exuberant spirit. The British paid little attention 
Title: Origins of the War of 1812
Content:  national honor in the face of what they considered to be British insults, such as the Chesapeake affair. The origins of the War of 1812 (1812-1815), between the United States and the British Empire and its First Nation allies, have been long debated. There were multiple factors that caused the US declaration of war on Britain:  American expansion into the Northwest Territory (now Ohio, Indiana, Michigan, Illinois, and Wisconsin) was impeded by Indian raids. Some historians maintain that an American goal in the war was to annex some or all of Canada, a view that many Canadians still share. However, many 
Title: Ohio in the War of 1812
Content:  During the War of 1812, Ohio was on the front lines in the conflict between the United States, Great Britain, Canadians, and the Native American allies of each side. Fighting raged in the northeastern section of the state and on the adjacent Lake Erie.
Title: 1812 in the United States
Content:  The following is a partial list of events from the year 1812 in the United States. After years of increasing tensions, the United States declares war on the British Empire, starting the War of 1812.
Title: 1810s
Content:  In 1812, the United States declared war on Britain in the War of 1812. The U.S. reasons for war included the humiliation in the "Chesapeake incident" of 1807, continued British impressment of American sailors into the Royal Navy, restrictions on trade with France, and arming hostile American Indians in Ohio and the western territories. United States President James Madison signed a declaration of war on June 18, 1812. The United States conducted two failed invasion attempts in 1812, first by General William Hull across the Detroit River into what is now Windsor, Ontario, and a second offensive at the Niagara peninsula. A major American success came in 1813, when the American Navy destroyed the British 
Title: Presidency of James Madison
Content:  trade. In response to persistent British attacks on American shipping and the British practice of impressment, the United States declared war on Britain, beginning the War of 1812. The war was an administrative morass, as the United States had neither a strong army nor financial system, and the United States failed to conquer Canada. In 1814, the British entered Washington and set fire to the White House and the Capitol. However, the United States won several notable naval victories and crushed the resistance of British-allied Native Americans in the West. Shortly after the American triumph at the Battle of New Orleans, the war ended with the ratification of the Treaty of Ghent, in which neither party made major concessions. Despite the lack of gains in the war, the timing of the treaty 
Title: Canadian units of the War of 1812
Content:  When the United States and the United Kingdom went to war against each other in 1812, the major land theatres of war were Upper Canada (broadly the southern portion of the present day province of Ontario), Michigan Territory, Lower Canada (roughly the southern part of present-day Quebec) and the Maritime Provinces of Nova Scotia, New Brunswick, Prince Edward Island and Cape Breton (colony between 1784 and 1820). Each of the separate British administrations formed regular and fencible units, and both full-time and part-time militia units, many of which played a major part in the fighting over the two and a half years of the war.
Title: War of 1812 (board game)
Content:  War of 1812 is a game that covers the war between the British and Americans in Canada and the Northern US.
Title: United States declaration of war upon the United Kingdom
Content:   An Act Declaring War between the United Kingdom of Great Britain and Ireland and the Dependencies Thereof and the United States of America and Their Territories was passed by the 12th United States Congress on June 18, 1812, thereby beginning the War of 1812. It was signed by James Madison, the 4th President of the United States.

Question: who did the united states fight in the war of 1812?
Answer: United Kingdom.