<P> Theories vary as to the causes of the catastrophic warfare and migration of many ethnic groups in the area . Populations had increased greatly in Zululand following the Portuguese introduction of maize in from the Americas in the late 17th century, reaching the inland around 1750 . While maize was more productive than the grains from native grasses, it required more water during cultivation . The agricultural surpluses and increased population enabled Shaka to raise a standing army of Zulus . By the end of the 18th century, the Zulus occupied much of their arable land . Declining rainfall and a ten - year drought in the early 19th century set off a competition for land and water resources among the peoples of the area . </P> <P> Other possible causes were the Zulus' adoption of new tactics and weapons during this period . Instead of using throwing spears, the Zulus used broad - bladed, stabbing spears known as iklwa, which were deadly in close combat . The Zulus also instituted a form of conscription, in which every man had to serve the king as soldier in special age regiments, known in English as impis . Many of the Nguni peoples adopted the same practice, putting most of their men under arms . This greatly expanded the scale of regional warfare . </P> <P> It is worth noting that there were three major ethnic groups which occupied the areas now known as Nquthu, Babanango, Empangeni, Mtubatuba, Hlabisa, Nongoma, Pongola, Vryheid, Melmoth and Mahlabathini--those ethnic groups were the Ngwane, the Ndwandwe and the Mthethwa . They were respectively led by kings Sobhuza of Ngwane, Zwide, and Dingiswayo and were the most powerful ethnic groups . The language now known as Zulu was spoken by the Ndwandwes . At that time the Zulus were a very weak ethnic group under the leadership of Senzangakhona . They spoke a thsefuya language in which "l" is pronounced as "y", so that' suka lapha', meaning' go from here', would be expressed as' suya yapha' . These three ethnic groups are to this day found in the same areas . The Zulus were a weak minority occupying a small piece of land in the area now known as Makhosini near Babanango . The Ikhoshlo side of Buthelezi led by Mvulane became instrumental in the defeat of Phungashe by Shaka . Mvulane's son Ngqengelele became Shaka's induna and chief advisor . Ngqengele's son, Mbangambi led his section of Buthelezis against Hhamu of Ngenetsheni . </P> <P> Oral history says that after the death of Mvulane, the younger brother of Phungashe, Mvulane's sons Khoboyela and Ngqengelele escaped being killed by Phungashe over their father Mvulane's estate and went to live with Senzangakhona and Ngqengelele . Most of the members of the Buthelezi ethnic group had left with Khoboyela and Ngqengelele . When Shaka attacked the Ngwane, Sobhuza's men were outnumbered by the combination of the Mthethwas, the Buthelezis under Ngqengelele and the Zulus . In summary, the causes of mfecane are; the need for land, population growth in Natal, the Boer trek, Shaka's military and expansionist strategy . In addition, the profitable slave trade through Delagoa Bay (modern day Maputo Bay) is another cause . </P>

How did strong centralised states develop as a result of the mfecane