How did Mahajanapada emerge from Janapada

The term "Janapada" literally means the foothold of a tribe. The fact that Janapada is derived from Jana points to an early stage of land-taking by the Jana tribe for a settled way of life. This process of first settlement on land had completed its final stage prior to the times of the Buddha and Pāṇini. The Pre-Buddhist north-west region of the Indian sub-continent was divided into several Janapadas demarcated from each other by boundaries. In Pāṇini's "Ashtadhyayi", Janapada stands for country and Janapadin for its citizenry. Each of these Janapadas was named after the Kshatriya tribe (or the Kshatriya Jana) who had settled there in Buddhist and other texts only incidentally refer to sixteen great nations (Solasa Mahajanapadas) which were in existence before the time of the Buddha. They do not give any connected history except in the case of Magadha. The Buddhist Anguttara Nikaya, at several places gives a list of sixteen great nations , Mahajanapada