Base your answer to the question on the time line below and on your knowledge of social studies. 1803 Louisiana Purchase Treaty established western boundary of United States. 1818 - Convention with Britain established northern boundary of Louisiana Territory. 1819 Adams-Onis Treaty granted Florida to United States. 1842 Webster-Ashburton Treaty established Maine-Canada border. 1846 - Treaty of Oregon established northern boundary of Oregon Territory: The time line shows that the major way the United States gained territory in the early 19^th century was through 1 war 2 diplomacy 3 executive orders