Q. Before ascending the throne, Balban was awarded the prestigious title of 'Ulugh Khan' (Great Khan) for his successful defense against which threat?
Answer: The Mongol invasions during the reign of Nasir-ud-din Mahmud
Notes: Balban was titled 'Ulugh Khan' due to his successful military leadership as Naib to Sultan Nasir-ud-din Mahmud in defending against the Mongol invasions. This honor recognized his role in safeguarding the Sultanate from external threats. Other events like the Bengal rebellion or Mewati conflicts either occurred later or were not the primary reason for this title.