under whose reign most of the remainder of modern-day Sudan was conquered. The Egyptian authorities made significant improvements to the Sudanese infrastructure (mainly in the north), especially with regard to irrigation and cotton production. In 1879, the Great Powers forced the removal of Ismail and established his son Tewfik Pasha in his place. Tewfik's corruption and mismanagement resulted in the 'Urabi revolt, which threatened the Khedive's survival. Tewfik appealed for help to the British, who subsequently occupied Egypt in 1882. Sudan was left in the hands of the Khedivial government, and the mismanagement and corruption of its officials. During the Khedivial period, dissent had spread due to harsh taxes imposed on most activities. Taxation on irrigation wells and farming lands were so high most farmers abandoned their farms and livestock. During the 1870s, European initiatives against the slave trade had an adverse impact on the economy of northern Sudan, precipitating the rise of Mahdist forces. Muhammad Ahmad ibn Abd Allah, the Mahdi (Guided One), offered to the ansars (his followers) and those who surrendered to him a choice between adopting Islam or being killed. The Mahdiyah (Mahdist regime) imposed traditional Sharia Islamic laws. On 12 August 1881, an incident occurred at Aba Island, sparking the outbreak of what became the Mahdist War. From his announcement of the Mahdiyya in June 1881 until the fall of Khartoum in January 1885, Muhammad Ahmad led a successful military campaign against the Turco-Egyptian government of the Sudan, known as the Turkiyah. Muhammad Ahmad died on 22 June 1885, a mere six months after the conquest of Khartoum. After a power struggle amongst his deputies, Abdallahi ibn Muhammad, with the help primarily of the Baggara of western Sudan, overcame the opposition of the others and emerged as the unchallenged leader of the Mahdiyah. After consolidating his power, Abdallahi ibn Muhammad assumed the title of Khalifa (successor) of the Mahdi, instituted an administration, and appointed Ansar (who were usually Baggara) as emirs over each of the several provinces. Regional relations remained tense throughout much of the Mahdiyah period, largely because of the Khalifa's brutal methods to extend his rule throughout the country. In 1887, a 60,000-man Ansar army invaded Ethiopia, penetrating as far as Gondar. In March 1889, king Yohannes IV of Ethiopia marched on Metemma; however, after Yohannes fell in battle, the Ethiopian forces withdrew. Abd ar-Rahman an-Nujumi, the Khalifa's general, attempted an invasion of