Introduction:
The small tribes of the earlier period that gave way to large kingdoms were called "Janapadas". These Janapadas were the precursors to the formation of larger political entities in ancient India. The transition from small tribes to large kingdoms marked a significant milestone in the political and social history of ancient India.

Explanation:
The process of urbanization and the emergence of settled agricultural communities led to the formation of small tribal societies. These tribes gradually evolved into larger political units known as Janapadas. Let's delve into the details of this transition:

1. Definition and Characteristics of Janapadas:
- Janapadas were territorial units that encompassed several villages and towns.
- They were governed by a king or a chieftain who exercised political authority over the territory.
- The Janapadas had their own administrative systems and laws to maintain order and control within their boundaries.
- Some prominent Janapadas included Magadha, Kosala, Vatsa, Avanti, and Kuru.

2. Factors contributing to the Rise of Janapadas:
- Agricultural Surplus: The shift from hunting-gathering to settled agriculture resulted in surplus food production, which allowed for the sustenance of larger populations and the growth of settlements.
- Trade and Commerce: The development of trade networks facilitated the exchange of goods and ideas, leading to economic growth and cultural interactions between different tribes and regions.
- Warfare and Conflict: Competition for resources, territorial disputes, and the need for defense against external threats necessitated the consolidation of smaller tribes into larger political entities.

3. Process of Transition:
- Initially, small tribal communities formed alliances for mutual protection and cooperation.
- Over time, these alliances evolved into larger political units, with a central authority governing the collective interests of the member tribes.
- The leader of the most powerful tribe or the most influential chieftain often assumed the role of the king or ruler of the Janapada.
- The Janapadas gradually expanded their territories through conquest, diplomacy, or assimilation of neighboring tribes.

4. Significance of Janapadas:
- The formation of Janapadas laid the foundation for the emergence of larger kingdoms and states in ancient India.
- They provided a framework for political organization and governance, establishing the concept of a centralized authority.
- The rise of Janapadas marked the beginning of a more complex socio-political structure, with increased social stratification and the emergence of specialized occupations.

Conclusion:
The small tribes of the earlier period that gave way to large kingdoms were known as Janapadas. These Janapadas played a crucial role in the political and social evolution of ancient India. The transition from small tribal societies to larger political units was a significant milestone, setting the stage for the formation of powerful kingdoms and states in the subsequent centuries.