Please read the following table in Markdown format and then answer the question according to the table. Table cells in one row are seperated by '|', and different rows are seperated by '
'.

Table:
| State (class) | Vacator | Reason for change | Successor | Date of successors formal installation |
| --- | --- | --- | --- | --- |
| Tennessee (1) | Vacant | Vacancy in term | Andrew Johnson ( D ) | October 8, 1857 |
| South Carolina (3) | Andrew Butler ( D ) | Died May 25, 1857 | James H. Hammond ( D ) | December 7, 1857 |
| New Hampshire (3) | James Bell ( R ) | Died May 26, 1857 | Daniel Clark ( R ) | June 27, 1857 |
| Texas (1) | Thomas J. Rusk ( D ) | Died July 29, 1857 | J. Pinckney Henderson ( D ) | November 9, 1857 |
| South Carolina (2) | Josiah J. Evans ( D ) | Died May 6, 1858 | Arthur P. Hayne ( D ) | May 11, 1858 |
| Minnesota (1) | New seat | Minnesota admitted to the Union May 11, 1858 | Henry M. Rice ( D ) | May 11, 1858 |
| Minnesota (2) | New seat | Minnesota admitted to the Union May 11, 1858 | James Shields ( D ) | May 11, 1858 |
| Texas (1) | J. Pinckney Henderson ( D ) | Died June 4, 1858 | Matthias Ward ( D ) | September 27, 1858 |
| South Carolina (2) | Arthur P. Hayne ( D ) | Successor elected December 2, 1858 | James Chesnut, Jr. ( D ) | December 3, 1858 |
| Oregon (2) | New seat | Oregon admitted to the Union February 14, 1859 | Delazon Smith ( D ) | February 14, 1859 |
Question:
Why did the change happen in the state where the formal installation happen on February 14, 1859?
Answer:
Oregon admitted to the Union February 14, 1859