Read the source given below and answer the following questions:
In Maasailand, as elsewhere in Africa, not all pastoralists were equally affected by the changes in the colonial period. In pre-colonial times Maasai society was divided into two social categories – elders and warriors. The elders formed the ruling group and met in periodic councils to decide on the affairs of the community and settle disputes. The warriors consisted of younger people, mainly responsible for the protection of the tribe. They defended the community and organised cattle raids. Raiding was important in a society where cattle was wealth. It is through raids that the power of different pastoral groups was asserted. Young men came to be recognised as members of the warrior class when they proved their manliness by raiding the cattle of other pastoral groups and participating in wars. They, however, were subject to the authority of the elders.
In pre- colonial times Massai society was divided into how many social categories?