The smaller, western strip of former German Kamerun occupied by Britain from 1916 and administered as two non-contiguous units (Northern and Southern Cameroons) alongside neighbouring Nigeria; a League of Nations mandate then UN trust territory.
Split by 1961 UN plebiscite: Northern Cameroons voted to join Nigeria (effective 1 June 1961), while Southern Cameroons voted to join the newly independent Republic of Cameroon (effective 1 October 1961).
The atlas holds 2 border frames for British Cameroons — the shape you scrub through changes in 1916 · 1934.
Same standard mandate-to-independence history used for French Cameroon; covers both British administrative zones and the 1961 plebiscite split directly.