European missionaries introduced Christianity to Senegal and the Casamance in the 19th century. It was only in the 1850s that the French began to expand onto the Senegalese mainland, after they abolished slavery and began promoting an abolitionist doctrine, adding native kingdoms like the Waalo, Cayor, Baol, and Jolof Empire. French colonists progressively invaded and took over all the kingdoms, except Siné and Saloum, under Governor Louis Faidherbe.