The Igbo people, historically spelled Ibo, are an ethnic group of southeastern Nigeria. They speak Igbo, which includes various Igboid languages and dialects. Igbo people are one of the largest ethnic groups in Africa. In rural Nigeria, Igbo people are mostly craftsmen, farmers and traders. The most important crop is the yam; celebrations are held annually to celebrate its harvesting. Other staple crops include cassava and taro. Before British colonialism, the Igbo were a politically fragmented group. There were variations in culture such as in art styles, attire and religious practices. Various subgroups were organized by clan, lineage, village affiliation, and dialect. There were not many centralized chiefdoms, hereditary aristocracy, or kingship customs except in kingdoms such as those of the Nri, Arochukwu, Agbor and Onitsha. This political system changed significantly under British colonialism in the early 20th century; Eze (kings) were introduced into most local communities by Frederick Lugard as “Warrant Chiefs”. The Igbo became overwhelmingly Christian under colonization. Chinua Achebe’s Things Fall Apart is one of the most popular novels to depict Igbo culture and changes under colonialism. By the mid-20th century, the Igbo people developed a strong sense of ethnic identity. Certain conflicts with other Nigerian ethnicities led to Igbo-dominated Eastern Nigeria seceding to create the independent state of Biafra. The Nigerian Civil War or the Nigerian-Biafran War” (6 July 1967 – 15 January 1970) broke out shortly after. With their defeat, the Republic of Biafra once again was part of Nigeria. MASSOB, a sectarian organization formed in 1999, continues a non-violent struggle for an independent Igbo state. Due to the effects of migration and the Atlantic slave trade, there are descendant ethnic Igbo populations in countries such as Cameroon and Equatorial Guinea, as well as outside Africa. Their exact population outside Africa is unknown, but today many African Americans and Afro Caribbeans are of Igbo descent. According to Liberian historians the fifth president of Liberia Edward James Roye was of Igbo descent.