The historiography of the period between Sudanese independence in 1956 and South Sudanese independence in 2011 has been dominated by the two lengthy periods of civil war, c. 1963–72 and 1983–2004. Most scholars have concentrated on explaining these conflicts, detailing the suffering and coping of southern Sudanese, and emphasising their alienation from a series of authoritarian regimes and brief unsatisfactory parliamentary governments in Khartoum. The first parliamentary period straddled the declaration of independence in 1956 and established a pattern of sectarian politics and unstable coalition governments, in which the dominant northern Sudanese political parties were united only in opposing the federal structures demanded by Southern politicians and other emerging regional parties. The promotion of Islamisation and Arabicisation in the south by these parliamentary governments and by the subsequent regime of General Abboud (1958–64) demonstrated the centralising, authoritarian tendencies of the northern riverain political elite. The mounting armed rebellion in the south was an initial focus for criticism of Abboud's military government, feeding into the discontent which drove the October Revolution of 1964. Yet it was another military ruler, General Numayri, who would succeed in negotiating a settlement with the leader of the southern Anyanya rebels, Joseph Lagu, in 1972. Numayri in turn provoked the outbreak of the second period of civil war in 1983 by increasing interference in the Southern Regional Government, culminating in the abrogation of the 1972 agreement and the breakup of the Southern Region.