Explanation: The Delhi Sultanate, established in the early 13th century, faced numerous challenges, including invasions from the Mongols. The Mongols, under the leadership of Genghis Khan and his successors, were a formidable force that swept across Central Asia and into the Indian subcontinent. The Mongol invasions posed a significant threat to the stability and security of the Delhi Sultanate.
During the reign of Alauddin Khalji (1296-1316), the Delhi Sultanate experienced a marked increase in Mongol attacks. Alauddin Khalji, known for his military prowess and administrative reforms, had to deal with multiple Mongol invasions. The Mongols, under the leadership of Kebek and later Duwa, launched several attacks on the sultanate, aiming to expand their territories and plunder the wealth of the region.
Alauddin Khalji responded to these threats by strengthening the defenses of the sultanate. He fortified the city of Delhi, constructed a massive wall around it, and established a strong military presence. He also reorganized the army, introducing new military strategies and tactics to counter the Mongol threat. The Mongols, despite their initial successes, were unable to make significant inroads into the sultanate due to Alauddin Khalji's effective military and administrative measures.
The reigns of other sultans, such as Qutb-ud-din Aibak and Muhammed Bin Tuglaq, did not witness the same level of Mongol attacks as Alauddin Khalji's reign. Aibak's reign was more focused on consolidating power and establishing the foundation of the sultanate, while Muhammed Bin Tuglaq's reign was marked by internal administrative challenges and less by external threats from the Mongols.
In conclusion, the period under Alauddin Khalji saw a significant increase in Mongol attacks on the Delhi Sultanate, making him the correct answer to the question. His reign is a critical period in the history of the Delhi Sultanate, marked by both military challenges and administrative reforms aimed at strengthening the sultanate's defenses against external threats.