Explanation: Delhi, as a significant city in medieval India, was a strategic and cultural center that attracted the attention of various invaders. Among these, the Mongols posed a constant and significant threat due to their military capabilities and the frequency of their invasions.
The Mongol Empire, founded by Genghis Khan in the early 13th century, was known for its rapid and devastating military campaigns. The Mongols were skilled horsemen and archers, and their military tactics were highly effective. They were able to conquer vast territories across Asia and Europe, and their invasions reached as far as India.
Delhi, being a key city in the Delhi Sultanate, was a prime target for the Mongols. The Mongol invasions of India began in the early 13th century and continued for several decades. The Mongols, under leaders like Genghis Khan and his successors, launched several raids into India, causing significant damage and disruption. The Delhi Sultanate, under various rulers, had to constantly prepare for and defend against these invasions.
The Mongol threat was not just a one-time event but a recurring challenge that the Delhi Sultanate had to face. The Mongols were known for their unpredictability and the speed of their attacks, which made them a constant source of concern for the rulers of Delhi. The Mongol invasions also had a significant impact on the political and military strategies of the Delhi Sultanate, leading to the strengthening of defenses and the development of military alliances.
In contrast, other options like the Turks and the Khilji dynasty were not constant threats. The Turks were a significant force during the early Delhi Sultanate period, but they were more focused on establishing and consolidating their rule rather than being a recurring threat. The Khilji dynasty, which ruled from 1290 to 1320, was a ruling dynasty rather than a threat itself. While the Khilji rulers faced various challenges, including Mongol invasions, the term "Khilji" does not represent a constant threat to Delhi.
Therefore, the Mongols were the constant threat to Delhi due to their military capabilities, the frequency of their invasions, and the strategic importance of Delhi as a target. This makes option C the correct answer.