History of slavery in Utah refers to slavery as it occurred in the borders of modern-day Utah. Under Spanish and Mexican rule, Utah was a major source of illegal slave raids by Mexican, Ute and Navajo slave traders, particularly on Paiute tribes. When Mormon pioneers entered Utah, they introduced African slavery and provided a local market for Indian slavery. Slavery was the de facto law based on Mormon beliefs on blacks until it was officially legalized in Utah Territory on Feb 4, 1852 with the passing of the Act in Relation to Service. It was repealed on June 19, 1862 when Congress prohibited slavery in all US territories. Today, slavery continues in Utah in the form of human trafficking and is very prevalent.