By the middle of the 1730s, Hussain Hotak had built up a substantial power base as the ruler of Herat and had been striving for some years to weaken Nader Shah's authority over present-day Afghanistan.

According to the Iranologist Laurence Lockhart, Nader Shah understood that he could fund his aspirations of expansion "with the spoils of India" because "the almost continual campaigns of the past few years had caused famine in Persia and brought her to the verge of bankruptcy."

"[9] According to the Iranologist Michael Axworthy, the aim of the invasion was because Nader Shah "needed a breathing space, for the country to recover, and a new source of cash to pay the army, before he renewed his attack on the Ottomans.

By the beginning of the 18th century, the Indian subcontinent was still a huge and prosperous agricultural economy, but becoming more and more divided , making it an alluring target for a conqueror short on finance.

In response, he sent an envoy to the imperial court, and expressed that his only wish was to do the Mughals a favour and rid them of the Afghans; how they had done more damage to India, and that the Kabul garrison's hostility forced him to fight them.

Nader marched swiftly through the steep path and outflanked the Mughal army at the Khyber Pass and annihilated it.

The city administrator attempted to fix prices at a lower level and Afsharid troops were sent to the market at Paharganj, Delhi to enforce them.

However, the local merchants refused to accept the lower prices and this resulted in violence during which some Afsharid troops were assaulted and killed.

When a rumour spread that Nader had been assassinated by a female guard at the Red Fort, some Indians attacked and killed 3,000 Afsharid troops during the riots that broke out on the night of 21 March.

Almost immediately, the fully-armed Afsharid Army of occupation turned their swords and guns on to the unarmed and defenceless civilians in the city.

These events were recorded in contemporary chronicles such as the Tarikh-e-Hindi of Rustam Ali, the Bayan-e-Waqai of Abdul Karim and the Tazkira of Anand Ram Mukhlis.

[15] Finally, after many hours of desperate pleading by the Mughals for mercy, Nader Shah relented and signalled a halt to the bloodshed by sheathing his battle sword once again.

It has been estimated that during the course of six hours in one day, 22 March 1739, approximately 20,000 to 30,000 Indian men, women and children were slaughtered by the Afsharid troops during the massacre in the city.

[19][20][21][18][page needed] But, still the yield of plunder seized from Delhi was so great that Nader stopped taxation in Persia for a period of three years following his return.

Nader Shah's victory against the crumbling Mughal Empire in the East meant that he could afford to turn to the West and face the Ottomans.

[23] According to Axworthy, Nader's Indian campaign alerted the East India Company to the extreme weakness of the Mughal Empire and the possibility of expanding to fill the power vacuum.

Axworthy claims that without Nader, "eventual British rule in India would have come later and in a different form, perhaps never at all – with important global effects".