President Polk dispatched John Slidell, a Louisiana lawyer, to Mexico City in the fall of 1845. Slidell was born in New York city in 1793 and had moved to New Orleans in 1819. There he had practiced law, served as a federal district attorney and a member of the U.S. House of Representatives from 1843 to 1845.
His assignment from Polk was to negotiate the following:
- Mexican recognition of the Rio Grande as the border between Texas and the United States
- American forgiveness of the claims by U.S. citizens against the Mexican government
- The purchase of the New Mexico area for $5 million
- The purchase of California at any price.
Mexican governmental affairs were in turmoil and the Slidell Mission was not received. Slidell returned to the United States and recommended to the president that strong action be taken against Mexico.
Later in 1853, he was elected to the U.S. Senate as a representative of Louisiana. He resigned in 1861 to support the Confederacy. During the War, he conducted diplomacy for the Confederacy in France, where he remained until the fall of the Empire in 1870 when he moved to Britain. He died there in 1871.