The answer to the blank space is The Indian Removal Act. This act was signed in 1830 and authorized President Andrew Jackson to remove southern Native American tribes from their territory in the Southeastern United States to the area near Mississippi River.
Though these tribes were recompensed for their lands, the tribes did not have a choice to stay. During the process of relocation, many Native Americans died, in an event that is now widely known as the Trail of Tears.