Concept:The Mahdist War began when Muhammad Ahmad declared himself the Mahdi and launched a revolt.Explanation:The Mahdist War was fought between the Mahdist Sudanese forces of Muhammad Ahmad and the Egyptian Khedivate, later joined by Britain.In 1881, Muhammad Ahmad publicly proclaimed himself the "Mahdi" of Islam and started his uprising.This rebellion, which began in the year 1881, marked the official start of the military conflict.The war later expanded when British forces became involved after the fall of Khartoum in 1885.Answer:B. 1881