The British had firmly established their position by the middle of the nineteenth century and a large part of India came under their direct rule. The areas that remained independent were indirectly under British influence. There are various reasons for the success of the British rule against Indian rulers and some of them are listed as follows:
There was a vacuum of power in India after the Mughal Empire got fractured falling under its own weight. Its various governors and rebel commanders established their superiority at different places and started fighting against each other. This gave the British the opportunity to establish their trading posts in India.
Flag followed the trade: These trading posts were used to store the goods and for that British built many warehouses, which gave them an excuse to build forts and to build up armies to "protect" them. The East India Company made treaties with most of the kings to keep them satisfied so that they would not try and fight against the British.
Lack of unity among Indian states - Even though there were powerful Indian states like Punjab, Mysore and the Marathas that ruled Indian subcontinent during the mid-19th century, many of them were fighting with each other for different reasons. They failed to perceive the danger arising from the East India Company and could not unite against a common foreign enemy.
British were strong at sea. The British came through the sea; they established their naval power in the Indian Ocean before coming to the Indian mainland. Since none of the Indian states had a strong navy to challenge the British supremacy, they had an easy run to establish themselves in the coastal regions of India.
Divide and Rule: The British took advantage of the situation as the Indian rulers failed to create a stable social, political and economic order. The British took advantage of the deep division of Indian, social, political and economic structure. They adopted the policy of ‘Divide and Rule,’ policy and played one state against the other. Slowly many Indian states had fallen prey to the British designs and were forced to fight with each other.
The British also took advantage of the people, training them to be soldiers and employing them for the British army; the new army was better trained and more disciplined then the Indian armies.
The British made use of their Indian troops sided with an Indian kingdoms in defeating its rivals. The British in fact, caused a total of 111 wars among the Indian states.
Technological and Military superiority: The Indian armies were badly-trained and poorly-paid was no match for the disciplined and well-trained British forces. The Indians were technologically backward as well.
In comparison the British had technological military and transportation superiority over Indians. The British had developed new techniques of warfare that was unknown to Indians. It was with the help of the Indian soldiers, the British were able to capture most of India.
The British army’s were a united lot and moved much faster under a unified command. The British would retaliate if their trading fort was attacked by some overconfident governor or prince.
These are some of the reasons of the success of the British against the Indian rulers that led to the establishment of the British rule in India.