The Delhi Sultanate (1206–1526) of India played a pivotal role in shaping the political, social, and economic landscape of the Indian subcontinent. Established by Qutbuddin Aibak in 1206, the Sultanate saw the rise of several dynasties including the Mamluks, Khaljis, Tughlaqs, Sayyids, and Lodi. This study analyses the factors which contributed to the rapid expansion and eventual decline of the Delhi Sultanate. It highlights how military prowess, administrative innovations, and religious policies enabled the Sultans to consolidate power over vast territories. However, internal weaknesses, administrative inefficiencies, economic turmoil, and external invasions, including Timur's raid and Babur's conquest in 1526, accelerated its downfall. The study also explores the impact of Mongol threats, shifting alliances, and rebellions that weakened central authority. Furthermore, it assesses the socio-cultural legacy of the Sultanate, including architectural advancements, Persian influence, and the integration of Islamic and Indian traditions.