Final answer:
John Slidell was sent to Mexico City in 1845 to negotiate a border dispute and acquire California and New Mexico territories.
Step-by-step explanation:
John Slidell was sent to Mexico City in 1845 to negotiate a Texas border at the Nueces River and buy California and New Mexico territories. His mission was to resolve the border dispute and expand the United States' territory. However, his mission was unsuccessful, and he was not able to achieve these objectives.
Learn more about John Slidell's mission in Mexico City in 1845