Question

By 1820, most American Indians east of the Mississippi River were

Answer 1

It is C. I hope this helps ;)

Answer 2

Okay so during the 1820s Andrew Jackson, the first democrat, was in charge and wanted to remove Indians from their lands. he forced them on the trail of tears in which the Indians were forced to relocate. The Indians were forced to move west of the Mississippi River because gold had been discovered in the Georgia area, from what I've learned in American history. We know that the Indians and Jackson's militia group fought many battles. The Indians, even though they had help from like the French or others, kept loosing battles. 
 
With what the summary I have provided my best guess is that They had been defeated by the US military.