Kamerun
Kamerun (modern-day Cameroon and parts of what is now eastern Nigeria) had a garrison of about 1,000 German soldiers supported by about 3,000 African soldiers. Initially, the British attacked out of Nigeria following three different routes east into Kamerun. However, all three columns were defeated by a combination of the terrain, rough trails, and ambushes by the Germans. The French attacked south from Chad and captured Kusseri. Early in September, a Belgian-French force (mostly from the Belgian Congo) captured Limbe on the coast. With the aid of four British and French cruisers acting providing naval gunfire support, together with an improvised flotilla of costal and riverine craft, the Allies captured the colonial capital of Douala on 27 September 1914. The German garrison at Garoua fell to the British in June 1915.
The only major center of German resistance was now Yaounda (modern-day Yaoundé), but the Allies had to wait until the dry season before the terrain allowed them to renew the offensive. The Belgian-French forces followed the German-built railroad inland, beating off German counterattacks along the way. By November, Yaoundé was captured. Most of the surviving German soldiers retreated into Spanish Guinea (modern-day Equatorial Guinea), which was neutral territory. There the Spanish interned them for the duration of the war. The last German fort in Kamerun (at Mora) surrendered in February 1916.
Read more about this topic: West Africa Campaign (World War I)