Spirituals (also known as Negro spirituals or spiritual music) is a genre of Christian music that is "purely and solely the creation" of generations of Black Americans,: 13, 17  which merged African cultural heritage with the experiences of being held in bondage in slavery, at first during the transatlantic slave trade—the largest and one of the most inhumane forced migrations in recorded human history, and for centuries afterwards, through the domestic slave trade. Spirituals encompass the "sing songs," work songs, and plantation songs that evolved into the blues and gospel songs in church. In the nineteenth century, the word "spirituals" referred to all these subcategories of folk songs. While they were often rooted in biblical stories, they also described the extreme hardships endured by African Americans who were enslaved from the 17th century until the 1860s, the emancipation altering mainly the nature (but not continuation) of slavery for many. Many new derivative music genres emerged from the spirituals songcraft.