The Zappo Zap were a group of Songye people from the eastern Kasai region in what today is the Democratic Republic of the Congo. They acted as allies of the Congo Free State authorities of the King of the Belgians, while trading in ivory, rubber and slaves. In 1899 they were sent out by the colonial administration to collect taxes. They massacred many villagers, causing an international outcry.
According to the missionary William Henry Sheppard, the Zappo Zap people all had tattoed faces and had filed their teeth to sharp points. They dressed only in two minute pieces of palm fiber cloth. They were armed with long spears and with poisonous and steel arrows. Their iron weapons gave them an advantage in warfare, and when armed with guns the advantage was decisive. The Songa people, to whom the Zappo Zaps belonged, also used battle axes (kasuyu or zappozap).
The Zappo Zaps worked as mercenaries for whoever was in power. They had been engaged in slave raiding long before the Europeans arrived, burning villages, partly eating bodies and selling hundreds of slaves to the Arabs each year in exchange for guns, ammunition and other manufactured goods. The Zappo Zaps did not restrict their cannibalism to ceremonial occasions, as in other cultures. Instead they hunted humans for food even when other game was plentiful. They considered human flesh a delicacy, and ate all parts of the body, even brains and eyeballs. They fried the meat in the same way as bacon.
In March 1883 Hermann Wissmann, the first European traveller in the region, gave the name "Zappo Zap" to a leader known as Nsapu Nsapu who ruled over the town of Mpengie, part of the Ben'Eki kingdom. This was a settlement with more than a thousand people, many of them slave warriors, to the east of the Sankuru River between Kabinda and Lusambo. The group were thriving through slave raiding and trading with caravans from the Arab and Swahili towns on the Lualaba River to the east and from Bihe in Angola to the southwest.
In 1883 Zappo Zap felt strong enough to challenge the king of the Ben'Eki, leading to a civil war that drew in all the slavers of the region. In 1886, he was forced to retreat to a location near Lusambo, where he built an impressive station. In 1887 he lost a battle on the right bank of the Sankuru and was forced to cross the river with his 3,000 followers. He met the Congo Free State commander Paul Le Marinel near Lusambo, with Chief Mukenge Kalamba of the Lulua, both retreating westward from the Lualaba.