"The British came neither as migrating hordes nor as armies seeking plunder, yet eventually they did more to transform India than any previous ruling power."Explain this apparent paradox.

This apparent paradox can be explained in the light of gradual and not sudden effects on political, economic, social and cultural spheres of India.
Political Effects
The political influence of British increased gradually and not suddenly. They came to India for trade and were lucky enough to get Mughal permission to trade and even luckier to find the country divided into numerous political divisions. They first served as allies of local Rajas and Nawabs; then became their virtual bosses and finally became their masters. Indians also were more comfortable with British hegemony rather than hegemony of their Indian neighbours. Gradually, the Indian people as well as royals started adopting European manners such as training troops, personnel management etc. Gradually, the British changed the political landscape with introduction of concepts like rule of law, equality before law, elaborate legislative process etc. Judiciary was codified in structure and functioning with system of courts and codification of laws. Modern military, police and judiciary were introduced by British in India.
Economic Effects
During Mughal era, India was world’s largest economy. Beginning with the dual administration of Bengal, it took many years for the economy to get totally devastated. East India Company diverted the agriculture by forcing the farmers to grow cotton and silk, indigo, tea and opium which were used by British for their own benefits. British were also able to divert the trade in their own side. The system of revenue collections such as permanent settlements further accelerated the drain of wealth. Frequent famines, followed by little relief works; almost negligible expenditure on public works; revenue collection with cruelty; artificial rising of prices; debt burden on Nawabs and Rajas; charging hefty war indemnities from defeated Rajas etc. were some of the reasons that gradually killed the very soul of Indian economy.
Social Effects
British introduced disruptions in Indian socio-economic system. The permanent settlement in Bengal, Bihar and Odisha reduced the smaller landlords to tenants and tenants to beggars. The rise of absentee landlords in the last few years of 18th century and beginning of 19th century broke the social links between cultivators and land lords. In Calcutta, a fashionable and intellectual society emerged made of upper Bengali castes. In other parts of India also, there was repression of the old aristocracy and rise of new middle and upper middle class deeply influenced by British.
Cultural Effects
The cultural effects were far reaching. The British started taking deep interest in Indology and orient, while Indians began to study European ways and thought. Some of them Indians went forward and made efforts to fuse the western ideas with Indian ethos. We note that previous conquerors had adopted the Indian culture and considered India as their home while British always remained an alien power due to their sense of superior culture, technological advancements. Nevertheless, the introduction of new ideas of enlightenment like humanism, rationalism etc. created a class of enlightened individuals in India, which led the movement against the social evils like sati, untouchability etc.