February 24, 1739, battle between the forces of Nadir Shah, an Iranian adventurer, and Muhammad Shah, the Mughal emperor, at Karnal, 125 km north of Delhi; the Mughals suffered a decisive defeat. Nadir led about 55,000 troops, and Muhammad 15,000, but both sides, especially the Indian, had large numbers of noncombatants. Nadir Shah had become the ruler of Persia by deposing the King in 1732.

Nadir began his invasion in 1738 AD by pursuing fugitives from Kandhahar to Mughal-held Kabul (both now in Afghanistan). The alleged violation of promises by Muhammad Shah, and the ill-treatment of his envoys by the Delhi court, served as the alleged cause for his invasion. Divided counsels prevented a Mughal stand until Nadir reached Karnal. Jealousy and rashness led to the Indian defeat, and the emperor was besieged in his entrenched camp. Nadir marched to Delhi and massacred its inhabitants on March 11. He left Delhi on May 5 with plunder, including the famous Peacock Throne of Shah Jahan and the Koh-i-noor diamond. The Mughal Empire never recovered from this blow to its prestige.