In 1756, Ahmad Shah Abdali invaded India once again and captured Delhi and plundered Mathura. Marathas became more powerful because of their collaboration with Imad-ul-Mulk, and dominated the whole of northern India. This was the peak of Maratha expansion, which caused great trouble for the Mughal Empire, already weak with no strong ruler. Relations between Alamgir II and his usurping vizier, Imad-ul-Mulk had now deteriorated. He was murdered by Imad-ul-Mulk. Alamgir II's son Ali Gauhar escaped persecution from Delhi, while Shah Jahan III was placed on the throne.