Shaka Zulu. In the early 19th century Shaka was chief of a small sub tribe in present day Natal. His lands were around 10 square miles and he ruled over no more than 1,500 people. Within 20 years he had conquered lands amounting to 11,500 square miles and ruled over more than a million people. He achieved this by radically changing military tactics and structure. Up until Shaka came on the scene battles between sub Saharan tribes were fairly ritualized with the throwing of long spears from distance a lot of chanting but little hand to hand combat and casualties were low. Rather like early ancient Greek battles.
Shaka changed this by inventing the short thrusting spear, making shields larger and invented independently the very Roman tactic of hooking the Shields of the opponent and thrusting the short spear in close combat. His troops were conscripted, fought in close order and were well trained. He developed the envelopment by pinning his enemy in the centre and sending the right wing around to attack from the rear. He perfected this to the double envelopment or horns of the bull. The British at Isandlwana were to discover just how devastating this tactic could be 40 or so years later. Shaka was a tyrant and ruled with a rod of iron killing over a million people during his reign. His brothers eventually did for him. The Zulus remained lord of their lands until 1879 and the Anglo/Zulu war.