The Underground Railroad was a network of secret routes and safe houses established in the United States during the early to mid-19th century. It was used by enslaved African Americans primarily to escape into free states and from there to Canada. The network, primarily the work of free African Americans, was assisted by abolitionists and others sympathetic to the cause of the escapees. The slaves who risked capture and those who aided them are also collectively referred to as the passengers and conductors of the Railroad, respectively. Various other routes led to Mexico, where slavery had been abolished, and to islands in the Caribbean that were not part of the slave trade. An earlier escape route running south toward Florida, then a Spanish possession, existed from the late 17th century until approximately 1790. However, the network generally known as the Underground Railroad began in the late 18th century. It ran north and grew steadily until the Emancipation Proclamation was signed by President Abraham Lincoln. One estimate suggests that, by 1850, approximately 100,000 slaves had escaped to freedom via the network.