The Battle of Karnal (24 February 1739), was a decisive victory for Nader Shah, the founder of the Afsharid dynasty of Iran, during his invasion of India. Nader's forces defeated the army of Muhammad Shah within three hours, paving the way for the Iranian sack of Delhi. The engagement is considered the crowning jewel in Nader's military career as well as a tactical masterpiece. The battle took place near Karnal, 110 kilometres (68 mi) north of Delhi, India.The battle was the culminating point of Nader Shah's invasion of the Mughal Empire. After his conquest of eastern Afghanistan and invasion via Kabul and Peshawar, Nader led his forces south towards the Mughal capital. At Delhi Muhammad Shah gathered an extremely large force with which he marched north before his cumbersome army ground to a halt at Karnal. Nader gave battle and won a crushing victory. In the negotiations following the catastrophic defeat, Muhammad Shah agreed to pay a large indemnity in exchange for maintaining his imperium over his lands. Nader however, forced the Mughal emperor to submit utterly and marched him to his capital, Delhi, where the Mughal treasury was plundered. An uprising against Nader's soldiers by Delhi's citizens ended in a bloody massacre where the entire city was sacked and looted. The enormous plunder gained in Delhi caused Nader to issue an imperial decree removing all taxes for a total of three years. The Persian army soon after departed leaving behind 30,000 dead. Muhammad Shah was also forced to concede all his lands west of the Indus which were annexed by Nader Shah.

As a result of the overwhelming defeat of the Mughal Empire at Karnal, the already declining Mughal dynasty was critically weakened to such an extent as to hasten its demise. According to Axworthy, it is also possible that without the ruinous effects of Nader's invasion of India, European colonial takeover of the Indian subcontinent would have come in a different form or perhaps not at all.