What was the main goal of the federal indian policy from the late 1880s to world war 2

When conducting research for forming a hypothesis, which practice should historians follow?

President nixon resigned from office in 1974 after he was informed that the senate would impeach him, as allowed in the constitution, for his actions in the watergate scandal. one of the key reasons that nixon’s actions became public was a) the freedom of press guaranteed by the first amendment. b) the right to confront witnesses as guaranteed by the sixth amendment. c) the limitation of judicial powers as defined in article 3 of the constitution. d) the prohibition against illegal search and seizure as guaranteed by the fourth amendment.

Who did the first work in creating vaccines