- Gombe slave-raids on the Tangale-Waja highlands (1810s–1890s) — Emirs Buba Yero and Suleimanu mount near-annual dry-season expeditions against the Tangale, Waja, Tula, Cham, Pero and Tera. The highlands hold; the slave-tribute economy of Gombe Abba is fed by these raids and by *jizya* from incorporated districts.
Gombe State · Crisis deep dive
Era −1 — Pre-colonial (pre-1900)
Methodology
Tier 1 · primary
Courts. Gazettes. National archives.
Tier 2 · corroborating
OCCRP. HRW. BudgIT. TheCable.
Tier 4 · tertiary, flagged
Wikipedia only where primary is pending. Always labelled.