India means Indian subcontinent minus Tibet and Baluchistan and regions to the east of arakanese ranges. Indian federal structures rose in this geography. The mountains of Hindukush (Known as Paariyaatra mountain by Hindus) is the natural, scientific, strategic and cultural frontier of India to north-west. Tibet is similar natural frontier of India to north. Forests of Iravaty river basin is natural frontier of India to east. The land enclosed within these geographical frontiers were called as India by outsiders and Bhaarata by the Insiders. The cultural operating system within this land is called as "Dharma" which is the unifying thread of otherwise apparently diverse cultures, communities, Jaatis (clans) residing and sharing this land with each other.Hindutva literally means Indian-ness. The core of India and Indianness is found in Vedas which is allegiance towards land of Sapta-Sindhu and culture and civilization of Sapta-Sindhu. The definition which Veer Savarkar gives for the word Hindu is
आसिंधु सिन्धु पर्यन्ता यस्य भारत भूमिका l पितृभू पुण्यभू च एव स वै हिन्दुरिती स्मृतः ll
- One who refers to the Indian subcontinent as Bhaarat and considers Bhaarat as his fatherland (or motherland) and most revered land (Punyabhoomi) is a Hindu.
This concept of revered land has its origin in the term of "Sapta-Sindhu" (7 rivers) which is widely cited in Vedic and post-Vedic literature.
This concept and high reverence of Sapta-Sindhu is central concept of Vedic literature. The most interesting part of Bhaaratiya civilization is the process in which the radius of this Sapta-Sindhu region increased and expanded with time.
The original Sapta-Sindhu region in early hymns of Rigveda comprises of 5 rivers of Punjab, Saraswati(in Rajasthan) and Kubha (Kabul) river in NWFP. This land is glorified as Sapta-Sindhu (Around 4000 BC to 1500 BC). The dwellers of this land are Arya people who are pure, rich, righteous and civilized men on earth who are Kavis (poets) composing beautiful literature and performing grand Yagnas to please their mighty Devas.
In later Rigveda (from 1900 BC to 1500 BC), in nadi-stuti sukta of 10th mandala, the Sapta-Sindhu region includes Ganga and Yamuna as well. Thus, now, this idea of Sapta-Sindhu, its culture and civilzation comprised of entire north Indian plains, from Bengal to NWFP.
In Puranic times post Rigveda (800 BC onwards), new Sapta-Sindhu concept became popular with time. This is seen in famous verse from Vishnu Purana (dated 400 to 500 BCE)
गंगेच यमुनेचैव गोदावरी सरस्वती l नर्मदे सिन्धु कावेरी जलेस्मिन सन्निधिम कुरु ll
From here on, the Sapta-Sindhu included the region of Ganga, Yamuna, Godavari, Saraswati, Narmada, Sindhu and Kaveri. Basically, entire Indian subcontinent.
Sapta-Sindhu is the term which gave birth to the word "Hindu". The Civilization of Sapta-Sindhu was referred to as Hapta-Hindu by Persians and other outsiders. The people of this region and culture, the Sapta-Saindhavas were referred to as hapta-Haindavas by Persians and other outsiders. All these terms are found in Zend Avesta of Zoroastrians. In all its context, Sapta-Sindhu has been the homeland of Sapta-Saindhavas (Bhaaratiyas/ Indians). This has been the Punya-Bhoomi (revered land) of them. This has been the Pitrubhoomi and Matrubhoomi for them.
Thus, the very concept and identity of India or Bhaarat originated from land of seven rivers and expands with the same. The concept of Bhaarat was Punjab and adjacent areas during Vedic war of ten kings where Sudas is a king of Bhaarata and Sapta Sindhu around 3000 BC. The concept of Bhaarat in Vishnupuran (around 400 BC) was same as pan-subcontinental identity of Sapta-Sindhu.
Dharma does not necessitate centralization of power. and hence since times of epics to modern day, India has always been a federation.