Answer:
1- The War of 1812 contributed to the growth of the United States by including new states because the reduction of British aid to Native Americans near the Mississippi River made white settlement easier.
2- The region that was a source of conflict between the United States and Great Britain was the Northwest.
3- The change in population between 1850 and 1860 was a result of a large wave of immigrants from Europe.
Explanation:
1- During the War of 1812, many native tribes collaborated with the British in exchange for economic aid and resources.
With the British defeat, the natives, who had been the main contenders of the Americans in the fighting (losing 10,000 men) were weakened in their position in their territories, to such an extent that those territories were effectively occupied and organized by representatives of the U.S.
2- The British claimed the entire Oregon Territory in the northwest of the current American territory, that is, they carried their claim south to the 42nd parallel north, which had been the limit agreed in 1819 between Spain and the United States in the Adams-Onis Treaty. The dispute between Great Britain and the United States was resolved peacefully, and until 1846 the United Kingdom and the United States, through the Anglo-American Convention of 1818, exercised a condominium over the entire Oregon Territory, further ensuring the inhibition of possible Mexican or Russian claims.
In 1846, Oregon's boundary dispute between the United States and Great Britain was resolved by the signing of the Oregon Treaty. The British gained exclusive possession of the land north of the 49th North parallel and the entire island of Vancouver , while the United States received the areas south of that line.
3- Throughout the nineteenth century the population of the United States grew extraordinarily because of the constant arrival of European immigrants, mostly young, coming mainly from Britain, Ireland and Germany.
Thus, the population went from less than thirteen million in 1830 to forty million in 1870.