According to James Olson – professor of History specializing on Ethnic Group studies, the Serer people "violently resisted the expansion of Islam" by the Wolof people in the 19th century, and then became a target of the 1861 jihad led by the Mandinka cleric Ma Ba Jaxoo. The inter-ethnic wars involving the Serer continued till 1887 when the French colonial forces conquered Senegal. Thereafter, the conversion of the Serer people accelerated. By early 1910s, about 40% of the Serer people had adopted Islam, and by 1990s about 85% of them were Muslims. Most of the newly converted Serer people have joined Sufi Muslim Brotherhoods, particularly the Mouride and Tijaniyyah Tariqas.