Which of the events listed had most affected the early development of the United States? Why do you think so? What were the effects of the event? A. The War of 1812
B. The Louisiana Purchase
C. The Monroe Doctrine

I would say B.. The Louisiana Purchase

Explanation:

Because of this, Americans traveled to this area to explore and in hopes to find riches. This also made the United States a larger country and encouraged people to travel to this new area. After the area was bought, more land was explored and found.

as general terms,  indian territory,  the indian territories, or  indian country  describe an evolving land area set aside by the  united states government  for the relocation of  native americans  who held  aboriginal title  to their land. in general, the tribes ceded land they occupied in exchange for  land grants  in 1803. the concept of an indian territory was an outcome of the 18th- and 19th-century policy of  indian removal. after the  civil war(1861–1865), the policy of the government was one of  assimilation.