Following Pinkerton's service with the Union Army, he continued his pursuit of train robbers, including the Reno Gang. He was hired by the railroad express companies to track outlaw Jesse James, but after Pinkerton failed to capture him, the railroad withdrew their financial support and Pinkerton continued to track James at his own expense. After James allegedly captured and killed one of Pinkerton's undercover agents (who was working undercover at the farm neighboring the James family's farmstead), he abandoned the chase. Some consider this failure Pinkerton's biggest defeat. He also opposed labor unions. In 1872, the Spanish Government hired Pinkerton to help suppress a revolution in Cuba which intended to end slavery and give citizens the right to vote. If Pinkerton knew this, then it directly contradicts statements in his 1883 book "The Spy of the Rebellion", where he professes to be an ardent abolitionist and hater of slavery. The Spanish government abolished slavery in 1880 and a Royal Decree abolished the last vestiges of it in 1886.