From Into Africa: The Epic Adventure of Stanley and Livingstone, by Martin Dugard (Broadway Books, 2003), Kindle loc. ~3170:
Mirambo was a handsome, powerful man who spoke in a quiet voice and was known for his generosity. He greeted visitors with a firm handshake and looked them directly in the eyes, inspiring confidence and a feeling of camaraderie. As a boy Mirambo had worked as a porter in the Arab caravans, and had adopted their manner of dress. The turban, cloth coat, and slippers he wore in his home gave him a cosmopolitan air.
The scimitar snug in the scabbard dangling from Mirambo’s waist was also Arab and hinted at the more ruthless side of the charismatic young leader’s personality. His date of birth was hard to pinpoint, but he was born the son of the Unyayembe region’s mightiest king, sometime in the days shortly after the Arabs opened the first Bagamoyo-to-Ujiji slave route in 1825. The Arabs had slowly stripped power from his father, stealing his lands and cutting him off from the ivory trade that ensured his wealth and kingdom. When his father passed on and Mirambo assumed the throne, the Arabs refused to recognize him as the premier African ruler of the region. Instead, they backed a puppet of their choosing named Mkasiwa.
To make matters worse, Mkasiwa was so emboldened by the recognition that he considered Mirambo to be a far-flung vassal. This made Mirambo furious. He didn’t immediately wage war on the Arabs, but expanded his kingdom among his own people, capturing village after village. He was a military genius and warred incessantly, excelling at the predawn surprise attack on an opponent’s weakest flank. His army of teenaged conscripts—married and older men were considered less aggressive and so were discouraged from fighting—would open fire with their single-shot muskets, then switch to spears as they overran villages in relentless waves. Once a village was conquered Mirambo celebrated the victory by looting the huts and splitting the booty with his army. The goats, chickens, women, and cloth were a reward for a job well done, and a fine enticement to wage war the next time Mirambo was in a warlike mood.
After the booty was split, Mirambo would round up the residents of the village and behead the village chief with his scimitar. Then he would anoint a favored and loyal warrior as the replacement. If, over the course of time, the new man failed to follow Mirambo’s directives to the letter, or attempted to rebel and form his own kingdom, a lesson was quickly taught. Mirambo would travel to the village and gather the citizens together. Then the warrior would be forced to kneel, and the scimitar would flash again. A new puppet would be installed, one who was more clear that Mirambo would tolerate no usurpation of his power. With this combination of battle, booty, and beheading, Mirambo rebuilt his father’s kingdom. The growth of his power slowly squeezed the lands surrounding Tabora, until the only corridor the Arabs controlled was the trade route between Tabora and Ujiji.
By the summer of 1871, just as Stanley arrived in Tabora, Mirambo’s strength was greater than ever—and still ascendant. Tabora was in a state of wartime preparedness as tension between Mirambo and the Arabs ratcheted upward. Both parties knew full well that the last African chieftain who’d confronted the Arabs, a man named Mnywa Sere, had been beheaded six years earlier. And with a lifetime of inequity to avenge, it made no difference to Mirambo that he was outnumbered three to one. The time had come to wage war. Mirambo began by harboring runaway slaves. It was a passive move, a taunt that got the attention of the Arabs. The second act of war, however, attacked the Arabs where it hurt them most: trade. Mirambo blocked the route from Tabora to Ujiji. Caravans trying to run the blockade would be plundered and murdered. Immediately, the Arabs called a council of war and made plans to attack. Fifteen days, they predicted, was all the time they would need to crush the infidel.