rival Shona states. The Portuguese also had vast estates, known as Prazos, and they used slaves and ex-slaves as security guards and hunters. They trained the men in military tactics and gave them guns. These men became expert elephant hunters and were known as the Chikunda. After the decline of the Portuguese the Chikunda made their way to Zambia. It is hypothesised by Julian Cobbing that the presence of early Europeans slave trading and attempts to control resources in various parts of Bantu Speaking Africa caused the gradual militarization of the people in the region. This can be observed with the Maravi's WaZimba warrior caste, who, once defeating the Portuguese, remained quite militaristic afterwards. The Portuguese presence in the region was also a major reason for the founding of the Rozvi Empire, a breakaway state of Mutapa. The ruler of the Rozvi, Changamire Dombo, became one of the most powerful leaders in South-Central Africa's history. Under his leadership, the Rozvi defeated the Portuguese and expelled them from their trading posts along the Zambezi river. But perhaps the most notable instance of this increased militarization was the rise of the Zulu under the leadership of Shaka. Pressures from the English colonialists in the Cape and increased militarization of the Zulu resulted in the Mfecane (the crushing). The Zulu expanded by assimilating the women and children of tribes they defeated, if the men of these Nguni tribes escaped slaughter, they used the military tactics of the Zulu to attack other groups. This caused mass displacements, wars and raids throughout Southern, Central and Eastern Africa as Nguni or Ngoni tribes made their way throughout the region and is referred to as the Mfecane. The arriving Nguni under the leadership of Zwagendaba crossed the Zambezi river moving northwards. The Ngoni were the final blow to the already weakened Maravi Empire. Many Nguni eventually settled around what is today Zambia, Malawi, Mozambique and Tanzania and assimilated into neighbouring tribes. In the western part of Zambia, another Southern African group of Sotho-Tswana heritage called the Kololo manage to conquer the local inhabitants who were migrants from the fallen Luba and Lunda states called the Luyana or Aluyi. The Luyana established the Barotse Kingdom on the floodplains of the Zambezi upon their arrival from Katanga. Under the Kololo, the Kololo language was imposed upon the Luyana until the Luyana revolted and overthrew the Kololo by this time