By the mid 18th century the last great Indian Kingdom, the Mughals were waning. In its demise the subcontinent became dotted with a great number of kingdoms and provinces, each with their own ruler, culture, language , religion, and more importantly politics. Foreigners have been in the Sub-Continent for a long time, the area had key ports, roads, and locations for trade. So its no surprise that a British company, the East India company, had set up posts and ports since the early 17th century. But throughout that century their main conflict would be with other European trade companies like the Dutch and Portuguese for control over the trade routes.

The First Catalyst would occur in the 7 years’ war where in India that Mughals backed the French against the Brits. After picking the losing side of that war the governor of the Bengal province was forced to hand over taxing rights to the British. In retaliation the rest of what was left of the Mughals attacked the British in the Battle of Buxar in 1764. That was also a loss for the native Indians, and in the aftermath the Mughal Emperor signed the Treaty of Allahabad, which gave the East India Company taxing, trading, and building rights in what was left of the Mughals lands, encompassing 1/8 of modern day South Asia.

This gave the British a foothold in which over the next hundred years they would expand over the rest of the sub-continent. In Mysore, with the Marathas, and the Sikhs the story is simple.The ruling king dies, the British promise a tertiary heir power, soldiers, and land if they agree to a treaty. This causes a succession war in which no matter what happens they win. They watched these empires crumble from the inside and swoop in to collect what is left. By 1820 they had control over much of central and south India. By 1857 by the time the Crown steps in to rule the sub-continent all off it was either under their control, or had some alliance to them.

Read these books for more information;

Raj, Kapil (2000), Colonial Encounters and the Forging of New Knowledge and National Identities: Great Britain and India, 1760–1850

Porter, Andrew (ed.) (2001), Oxford History of the British Empire: Nineteenth Century