All these kings had Marriage relation amongst themselves. Gujart Kings had Rajasthani Queen, Mysore king's wife was from Kathiyawad (Saurashtra Region of Gujarat). Ramji's wife Mata sita was from Nepal. All were relatives. Because of vast geographical area and diverse culture, there were many kingdom.
Kingdom of Chandragupta had many areas under his reign beyond today's India. His kingdom fulfills most of the criterion you noted. So as the case with Samudragupta and Lalitaditya Muktapid who rulled many parts of Today's China and Russia.
Race, Ethnicity and Language is a L**D European concept for a nation. India with over 28 languages and over 700 dialects is a much united nation than 26 Arab nations with same language, ethnicity and race.