Explanations:Delhi, the capital of India, has a long and complex history, especially during the medieval period. The city was a significant center of power and was frequently threatened by various invaders. Among these, the Mongols were a constant and significant threat to Delhi.
The Mongols, under the leadership of Genghis Khan and his successors, were known for their military prowess and expansive conquests. They established the largest contiguous empire in history, stretching from Eastern Europe to East Asia. The Mongol Empire's expansion brought them into contact with the Indian subcontinent, particularly the region around Delhi.
The Mongols conducted several raids and invasions into the Indian subcontinent, which posed a significant threat to the stability and security of the Delhi Sultanate. The fear of Mongol invasions was so pervasive that it influenced the military and administrative policies of the Delhi Sultanate. For instance, Alauddin Khilji, a ruler of the Delhi Sultanate, took several measures to strengthen the defenses of Delhi and the surrounding regions to counter the Mongol threat.
While other groups, such as the Turks, also posed threats to Delhi, the Mongols were a constant and significant danger due to their military capabilities and the fear they instilled. The Turks were more associated with the establishment and expansion of the Delhi Sultanate, rather than being a constant threat. The term "Sultan" refers to a title, not a specific group, and the Khilji dynasty was a ruling dynasty in Delhi, not a threat to it.
Therefore, the Mongols were a constant threat to Delhi, making them the correct answer in this context. Understanding the historical context and the specific threats faced by Delhi during the medieval period is crucial for comprehending the geopolitical situation of the time.