Zulu Warfare replaced skirmishing with shock tactics, analogous to ancient Greek hoplite warfare, which allowed them to sweep away the other Nguni tribes — until the British arrived:
The Southern Nguni Tribes became agriculturalists in the 19th century. Many were migrants from the intial exodus. They abandoned their pastoral economy and switched to agriculture along the coast. They began growing corn. Corn was a new crop from the Americas and was especially valuable as it grew in more adverse conditions than wheat and produced more calories per acre. This allowed an unprecedented population boom.These Nguni tribes in the south were regimentized into the British Army. They were provided rifles, uniforms, and training. British officers led these units, with Indian NCOs, and Nguni conscripted riflemen, which more or less reflected the racial stratification in Africa under colonial rule.
The Nguni and British military defeated the Zulu Empire through superior firepower. It was not just the rifles though. The British used the same concept of heavy infantry and shock tactics as the Zulus, so they were not intimidated by this form of combat. While rifles were useful for ranged combat, the real advantage was the close order formations of the British combined with the steel bayonet. Rifles reduced the Zulu numbers and the British could stand their ground and win the ensuing melee.