In 1296 Alauddin became the sultan after Malika Jan the widow of Jalaluddin and her younger son Qadir Khan left Delhi. He also exterminated the old Balbani and Jalali nobles. The reign of Alauddin Khilji marks the zenith of the power of the Delhi Sultanate. In 1297 he set off for conquering Gujarat. He sent an expedition under Ulugh Khan and Nusrat Khan to Gujarat. On the way Ulugh Khan conquered Jaisalmer. During the plunder of the rich port of Cambay Alauddin's commander Nusrat Khan acquired a Hindu turned Muslim slave Kafur who later on rose to become a great military general and the Malik Naib of Alauddin. After the conquest of Gujarat Alauddin sent an expedition under Ulugh Khan and Nusrat Khan to Ranthambhore. However they were beaten by the Rajputs and Nusrat Khan died. Alauddin went to Ranthambhor and annexed it in 1301. The next expedition was sent to Mewar and after the siege of 8 months he captured Chittor in 1303. The government of Chittor was put in the hands of Khizr Khan, the eldest son of Alauddin. Chittor was renamed as Khizrabad after the name of Khizr Khan. In 1305 Alauddin sent Ain-ul-Mulk Multani for the conquest of Malwa which was placed under the governorship of the latter. By the end of 1305 the whole of Northern India fell into the hands of Alauddin and he directed his attention to the conquest of Deccan.
Between 1307 and 1312 he began the southward expansion of his empire. He invaded Devagiri in 1306-07 AD. The immediate cause for this was unduly long delay in sending the annual tribute. In 1309 the Kakatiya kingdom was attacked and its ruler Pratap Rudra Deva accepted the suzerainty of Delhi and surrendered vast treasures. The next expedition was against Vir Ballala III the Hoysala ruler in 1311. His capital Dwarsamudra was captured. The whole of Deccan was forced to acknowledge the supremacy of Alauddin. His motives were to secure the immense wealth and to force the southern states to accept the suzerainty of the Sultanate. He had to face more than dozen invasions. These invasions started from the end of 1296 and continued upto 1308.The Mongols threatened not only Punjab,Multan and Sindh but even Delhi and the Ganga-Yamuna Doab. This grave crisis compelled him to take strong measures for the protection of the northwest frontier. The 20 years of his rule came to an end with his death on 2nd January 1316 AD.
Alauddin Khilji after assuming power directed his attention towards the Rajputs. The Rajput rulers of Gujarat, Ranthambhore, Mewar and Malwa became the targets of attack. The Rajput state of Ranthambhore became the target as the state has given shelter to some Mongol fugitives who had revolted during the Gujarat campaign. The Rajputs gave resistance to the army with siege of the fort lasted nearly a year but ultimately captured through the treachery of the minister on the Hammira Deva. The conquest of Ranthambhore was followed by attack on Chittor the capital of Mewar.Mewar was the most powerful Rajput state.
Khilji defeated Ratan Singh the ruler and occupied Mewar.The conquest of Gujarat, Ranthambhore and Mewar broke the back of Rajput power and resistance in North India. The sultan’s army conquered Malwa with its cities of Ujjain, Mandu, Dhar, Champaner.Several factors helped Alauddin Khilji in crushing the Rajputs. None of the Rajput states were strong when dealt by one by one by the sultan. The lack of unity among the Rajputs helped the forces of Khilji. The clannish rivalries and defection and treachery on the part of their own associates or officers of high rank helped Khilji to defeat the Rajput rulers of North India. AlauddinKhilji showed lack of political foresight when he tried to subjugate the rulers through force. He ordered massacre of general public. The cruel and humiliating treatment given to the defeated Rajput rulers and utter disregard shown to their religious sentiments alienated the support of them. He failed to win the confidence and cooperation of the people and therefore after his death one by one Rajput states slipped out of control of Delhi sultanate.
After consolidating his position in North India Alauddin Khilji embarked upon expanding his power to the Deccan and SouthIndia. TheYadavs of Devagiri, the Kaktiya of Warangal, the Hoyasalas of Dwarasamundra and the Pandayas of Madura dominated the Deccan region. Their existed an atmosphere of hostility between these rulers. Alauddin Khilji exploited this lack of unity among the rulers to a great extent. Malik Kafur the commander in chief of the sultan’s forces conducted successful campaigns against all these rulers. The Deccan policy of Alauddin Khilji was highly successful and produced number of significant results. He was the first sultan to establish his sway over North India and Deccan. These campaigns paved the way not only for the spread of Islam but also for the cultural diffusion from the north to south. These campaigns improved the transport and communication facilities pan India. His campaigns also helped in spread of Bhakti movement from South India to North India and Sufi movement from North India to the South India. They also exposed the weakness of South Indian rulers that led to victory of Alauddin Khilji. The most significant impact was that of establishment of the Vijaynagar Empire in South India.
Alauddin Khilji had to face more than dozen Mongol invasions. He took effective measures like repairing old forts in Punjab, Multan and Sindh and new forts were also built. These forts were garrisoned and equipped with troops. The most capable and trusted generals were placed in charge of these forts. New workshops were commissioned to manufacture arms and weapons. A highly efficient spy system was introduced and this enabled the sultan to get information about the activity of the Mongols. He struck terror in the hearts of Mongols by inflicting the most barbaric and brutal punishments. This made people confident of the ability of the sultan to protect them from any external danger. The successful Mongol policy of the sultan provided a secure frontier to his empire. It enhanced the power and prestige of the army. This prompted the sultan to introduce his market measures to serve the material comforts of his soldiers. Alauddin Khilji enforced highly centralized autocratic rule with all powers resting in him.