In 1738, the Persian leader Nadir Shah Invaded the Mughal Empire. Then, in 1739, he defeated Muhammad Shahs forces at Karnal. After that, he captured and attacked Delhi, taking over territories west of the Indus.
Nadir Shah did not intend to make himself emperor, but to win as much booty as possible and after 2 months he took huge amounts of gold, jewels and the peacock throne. He also took the prestige of the Mughals and showed everyone how weak the Mughals actually were.
The marathas formed a Hindu empire in southern India and were a constant source of difficulty for the Mughals.
Aurangzeb spent over years trying to defeat the Marathas, yet still after their death they continued to take land from the Mughals.
In 1737 the Marathas defeated the Mughal army and plundered Delhi and by the middle of the 18th century, the Marathas had replaced the Mughals as the most powerful force in India.
In 1747, an Afghan general, Ahmed Shah Durrani attacked Kabul, Peshawar and Lahore. By 1749, he had control over Punjab, and by 1756, he had Kashmir and Multan.
The weakness of the Mughal Empire can be seen by the fact that the Mughals were unable to to stop Maratha or Afghan expansion. It was actually Ahmed Shah Durrani who defeated the Marathas in 1761 at the battle of Panipat.