The main supporter of the principle of One Nation, One State is J.S Mill.

J.S Mill was a prominent philosopher and political economist of the 19th century. He is known for his influential works on liberty, utilitarianism, and representative government. Mill advocated for the principle of One Nation, One State, which emphasizes the unity and cohesion of a nation under a single political entity.

Below are the key points explaining why J.S Mill is the main supporter of the principle of One Nation, One State:

1. Definition of One Nation, One State:
- One Nation, One State refers to the idea of a unified and indivisible nation-state, where all citizens are equal and share a common identity.
- It implies the absence of internal divisions or separate political entities within the nation.

2. J.S Mill's political philosophy:
- Mill believed in the importance of a strong and centralized government to maintain social order and stability.
- He argued that a unified nation-state would be better equipped to protect individual liberties and promote the general welfare of its citizens.

3. Mill's support for a centralized government:
- Mill considered a centralized government as essential for efficient administration and the implementation of uniform laws and regulations.
- He believed that a strong central authority could prevent conflicts and tensions arising from regional or local differences.

4. Opposition to federalism and decentralization:
- Mill criticized the concept of federalism, which involves the division of power between a central government and regional authorities.
- He argued that federalism could lead to fragmentation and hinder the progress of a nation.

5. Utilitarian perspective:
- As a utilitarian, Mill focused on maximizing the overall happiness and well-being of society.
- He believed that a unified nation-state would enable the government to pursue policies that benefit the majority of citizens.

In conclusion, J.S Mill is the main supporter of the principle of One Nation, One State. He believed that a strong and centralized government would ensure social order, protect individual liberties, and promote the welfare of the entire nation. Mill's ideas on the importance of unity and cohesion align with the principle of One Nation, One State.