Modern Indian History
What was the single most significant contribution of Sardar Vallabhbhai Patel to Indian History?

As President of the Indian National Congress he engineered the passing of the Quit India Resolution
He was the leading light of Mahatma Gandhi's NonCooperation and Civil Disobedience Movements
As the Home Minister of free India he brought about the integration of 600-odd Indian States with the Indian Republic
He was responsible for the acceptance of the Mountbatten Plan by the Congress