Regions developed due to shared commonalty amongst the people like language, traditional rituals, and food habits. The traditions we follow have evolved through the intermingling of cultures. Language ties people together as a community more strongly than any other factor.
Earlier, all texts were written in Sanskrit. In the 9th century, Chera Kingdom of Mahodayapuram, first time, used a regional language, Malayalam, for administrative purposes, giving it the same position of power and respect as Sanskrit.
Shared religious traditions bring people together, especially if these traditions have the backing of the region’s rulers. The deity at Orissa was originally a local god who later identified as Vishnu. Realizing the important role of Vishnu in culture, King Anantavarman of the Ganga Dynasty constructed a temple for Purushottama Jagannath at Puri.
Another factor that brings people together is their shared values like, the Rajputs of Rajasthan speak different languages. However, the factor uniting them is their valour.