The reasons for European annexation of Cameroon were generally the same as the reasons for the Scramble for Africa in general. Some major reasons:
1. Resources. The African continent had many resources, especially mineral and agricultural, that were not available to the various European countries that participated in the Scramble.
2. Markets. It was hoped that having colonies would give each "mother country" a captive market for its goods -- one where only it could sell. This would help the European country's economy.
3. Strategic positioning. In these days, warships needed to be refueled relatively often and there were, of course, no airplanes, missiles, etc. So the only way for a country to be able to use military force in faraway regions was to have bases around the globe. Having colonies in Africa allowed this.
4. (And this may be the most important.) Prestige. If one country has a lot of colonies, then any country that doesn't have them looks weak (or at least weaker than those that did have them). As the previous answer indicates, this was a major reason for German annexation of Cameroon. Historians believe that this psychological need to keep up with the other countries was a huge factor in causing the Scramble.
As far as impacts go the colonization that followed the Scramble:
1. Hurt the colonies' economies. That's because their resources were being used to help the European countries rather than themselves.
2. Made it harder for them to do well once they became independent. One reason for this is that their economies were set up only for the benefit of the Europeans and this made them poorer than they might otherwise be. Second, the Europeans weren't interested in educating the Africans or in setting up democratic institutions. This is part of the reason why most African countries have had a hard time becoming stable and democratic.
The area that is now Cameroon had been a trading route with Europeans since the 15th century. England had already established several treaties with the Douala chiefs in the 1870s, but had not taken specific action to officially make the area a part of the British empire. German Chancellor Bismark sent a representative to the Sahara in 1884 and treaties were signed with the kings of Douala, Bimbia and Batanga, creating the German protectorate of Kamerun. The move by Germany was primarily a power play to establish colonies in North Africa as a response to Britain's growing worldwide colonization.
There were goods of high demand available there such as ivory.
They wanted to occupy the Cameroon territory due to fertile soil
They wanted to create an empire in and/or from Africa.
britain france and germany scrambled fir cameroon because,
-cameroon had good harbour and naval facilities like the ambas bay and the duala port which each of them wanted to control
-the presence of valuable products in cmeroun like ivory, made the europeans to scramble the territory.these goods were highly demanded in europe
-each of them wanted to acquire large potions of the cameroun territory especially the interior whiwc had fertile soil.they wanted to open large plantations to plant tropical crops like cocoa and coffee,highly demande in europe
-europeans wanted new markets to sell their excess manufactured goods
-the desire to create empires in africa also motivated the scramble for cameroon .france for example,wanted to create an empire in french equatorial africa,including africa