<span>inflicting further harm on them</span>
The last country in the world to challenge the United States control of Oregon was Great Britain. Oregon was won in the War of 1812.
Is this multiple choice? If not, i'd say that it is important for a historian to be sure of the authenticity of a primary source because a primary source needs to be proven to be accurate. It is important to study and make sure the source is authentic because the accuracy must be proven