The tutsi and hutu originally considered themselves a single group of people differing primarily by occupation; however, the belgium colonial administration began treating the pastoral tutsi people as different and superior to the hutu farmers. eventually, these two groups of people began to see each other as different as well. this is an example of

Ethnogenesis.

Explanation:

Ethnogenesis may be defined as the development and formation of the ethnic group. The inside and outside identification is important for the development of ethnogenesis.

Hutu and Tutsi considerd and treated unequally from each other. Earlier, they were considered a single group of people. Tutsi become superior farmer than Hutu. On the basis of ethnogenesis, they will see each other as different. Ethnogenesis includes the development of new emergence of social group and can be identify as cohesive identity.

Thus, the answer is ethnogenesis.