American History: Why did Mexico not join the Confederacy during the Civil War?

Today marks the anniversary of the surrender of Robert E. Lee's Confederate Army. (The entirety of the Confederate Army was made up of several smaller armies with Lee's being the largest. The others followed suit over the next 16 months.) When the fighting was over someone asked President Lincoln, "How did you keep Mexico from joining the Confederacy?" President Lincoln's answer was simple.

"Thomas Corwin."

Corwin was born in Kentucky, but grew up in Lebanon, Ohio. He served as a wagon boy in the War of 1812 (a nickname that would follow him. We have a piece of folk art of him with the same name) and would later establish a law practice with Durban Ward. 

Corwin went on to serve Ohio politically in the Ohio House of Representatives, the Governor of Ohio, and as a US Senator. Also known as the Great Orator, Corwin was said to be quite eloquent in his speeches and as "a born humorist" (according to peer, Benjamin Perley Poore). As a senator, he was being groomed for the Presidency but his outspoken stance opposing the Mexican-American War all but doomed his political career. Under the newly elected President Abraham Lincoln however, he was appointed Minister to Mexico due to his now strong relationship with the country's leadership developed from Corwin taking his believed in yet unpopular stance on the Senate floor despite the consequences to his political career.

Though the Confederacy courted Mexico several times throughout the Civil War, Mexico always refused due to their relationship with Corwin.

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