The Knights of the Golden Circle, which you may recall from Nicholas Cage’s movie National Treasure 2: Book of Secrets, was a secret society that envisioned the creation of a vast slave-based Southern Empire in Central America and the Caribbean.
In the 1850s, the filibuster William Walker had conquered Nicaragua, The Directory had tried to acquire Cuba from Spain, and Gov. John Quitman of Mississippi resigned after backing Narciso López’s failed attempt to conquer Cuba:
“The primary economic and political goal of this organization was to create a prosperous, slave-holding Southern Empire extending in the shape of a circle from their proposed capital at Havana, Cuba, through the southern states of the United States, Mexico, the Gulf of Mexico, the Caribbean, and Central America. The plan also called for the acquisition of Mexico which was then to be divided into fifteen new slave-holding states which would shift the balance of power in Congress in favor of slavery.
Facing the Gulf of Mexico, these new states would form a large crescent. The robust economy the KGC hoped to create would be fueled by cotton, sugar, tobacco, rice, coffee, indigo, and mining. These seven industries would employ slave labor.”
The Republic of Yucatán never joined the Confederacy. The U.S. Senate considered Yucatán annexation though at the end of the Mexican War. John C. Calhoun was opposed to annexation because he considered the area worthless.
The Confederacy was unable to defend its own national borders, control its own rivers and ports, and assert its own claim to Kentucky, Arizona, and New Mexico. For practical reasons, the Davis government was in no position to fight a two front war with Mexico and the United States, much less challenge the Royal Navy for control of the British West Indies.
In spite of this, a real historical opportunity did arise for Jefferson Davis (who had been an ardent Caribbean expansionist in the Senate) and the Confederacy to expand the “Golden Circle” into Northern Mexico:
“In late spring 1861, a Confederate agent tried unsuccessfully to encourage the eastern state of Veracruz to start a pro-independence campaign against the Mexican government. In the summer of the same year, Jefferson Davis turned down the offer of Santiago Vidaurri, governor of Nuevo León and Coahuila, to annex his provinces to the Confederacy, in return for troops. Davis dismissed the move as “imprudent and impolitic.”
The Mexican states of Tamaulipas, Nuevo León, Coahuila, and Veracruz would have been the first targets of Confederate national expansion. It is not far fetched to imagine a victorious Confederacy annexing Cuba and at least a few of these northeastern states from Mexico.