Why do we see the colonies switch from the use of indentured servants to the use of slaves? help please​

Match these items. 1 . stephen douglas published "north star" 2 . frederick douglass first african slaves arrived in jamestown 3 . crittenden compromise proposed kansas-nebraska act 4 . republican party extend 36° 30' line to california 5 . abolitionists servitude in exchange for passage to the united states 6 . indentured struggle between proslavery and antislavery groups 7 . jefferson davis formed to prevent spread of slavery 8 . "bleeding kansas" wanted slavery abolished 9 . uncle tom's cabin president of confederacy 10 . 1619 harriet beecher stowe