The process of British conquest of various parts of India extended over a period of nearly a century. The English suffered many diplomatic failures and some military but ultimately emerged victorious. A number of causes explain the victory of the British against their Indian adversaries.
The British were superior in arms, military tactics and strategy. The firearms used by Indian powers in the 18th century were slow firing and cumbersome and were outclassed both in quick firing and in range by European muskets and cannons used by the English. Again European infantry could fire three times more quickly than the heavy Indian forces. Many Indian rulers including Nizams, the Mysoreans and the Marathas imported European arms, employed European officers to train their troops in the use of European arms. Unfortunately Indian military officers and the rank and file could never rise above the level of amateurs and as such could not be match for English officers and trained armies.
The English had the advantage of military discipline. The company ensured loyalty of sepoys by strict discipline and regular payment of salaries. On the other hand most of the Indian rulers suffered the chronic problem of lack of means to pay salaries; some of the Maratha chiefs had to divert their campaigns for collecting revenues on personal retinues or mercenary soldiers who were deficient in military discipline and could mutiny or desert to the enemy when victory seemed doubtful.
The English had the advantage of civil discipline of the Company's servants. Men of discipline without any hereditary connections or ties directed the Company's army. Further European military officers were given command of armies only after rigorous discipline; they were reliable as well as skillful and were given overall direction of affairs. In contrast Indian military command was usually given on caste basis to relatives whose military competence was doubtful and who could prove refractory or disloyal to sub serve their personal ambitions.
The brilliant leadership gave the English another advantage. Clive, Warren Hastings, Elphinstone, Munro, Wellesley, Lord Hastings and Dalhousie etc. displayed rare qualities of leadership. They had the advantages of a long list of secondary leaders like Lord Lake, Arthur Wellesley who fought not for the leader but for cause and the glory of their country. The Indian side too had brilliant leaders like Haider Ali, Tipu Sultan, Scindhia, Nana Phadnavis and Ranjit Singh etc. but they more often lacked a team of second line trained personnel. Indian leaders were fighting against one another as against the British.
The British were superior in economic resources. The East India Company never ignored the trade and commerce. Towards the end of the 18th century the company’s foreign trade crossed 10 crores dollars. The East India Company earned enough profits in India to pay dividends to their shareholders and finance their military campaigns in India. England was also earning profits from her trade with the rest of the world. These natural resources in money and troops were available to the British in India in times of need thanks to the advantage of superior sea power that Britain possessed.