During James K. Polk's term, America’s territory extended across the continent and grew by more than one-third. These are some of Polk’s contribution to the territory of the US. Thank you for posting your question. I hope that this answer helped you. Let me know if you need more help.
James K. Polk was president in the 1800s, and he's responsible for really expanding the size of the United States by adding the southwestern states such as California, New Mexico, Arizona, Nevada, and Texas.
