Nadir Shah of Persia entered India in 1739, defeated the Mughal army at Karnal in a single afternoon, occupied Delhi and ordered a general massacre in the city after a riot. He took the Peacock Throne, the Koh-i-Noor and a treasure so large that he remitted taxation in Persia for three years.
The road out was through the Punjab. Sikh jathas, then a hunted and dispersed body, attacked the baggage train on the crossings of the rivers and took back part of the plunder and a number of the captives.
The Persian account attributed to Nadir asks the governor of Lahore who these men are, and records the answer that they are faqirs who live in the saddle and whose houses are their horses. It is quoted in every Sikh history and its provenance is not secure.
Najabat's Nadir Shah di Vaar, a Punjabi war ballad written soon after, is one of the earliest surviving pieces of Punjabi historical verse and treats the invasion from the ground.
The invasion broke the Mughal empire's remaining prestige. Everything in Punjab for the next sixty years follows from that.
He came down through Kabul and Ghazni, took Peshawar and crossed the Indus at Attock. Zakariya Khan, governor at Lahore, gave battle at Shahdara, was beaten, and was left in place as governor by the invader, which is a fair measure of what the Mughal writ in Punjab was worth by then.
The plunder went out on thousands of animals and took weeks to move. A column that long, crossing five rivers in the hot weather with a treasure on it, is why the return march and not the battle is what the Punjabi accounts remember.
He was killed by his own officers in 1747. Ahmad Shah Abdali, who had commanded under him, took the eastern half of what he had held and came back into Punjab nine times over the next twenty five years. That is the real inheritance of 1739.