Conquest of Gujarat:
After a successful repulsion of the invasion of the Mongols, Malik Sadi was sent to conquer Gujarat as it had broken off all her relations with the Sultanate of Delhi after the death of Mubarak Shah Khalji.
Malik Shadi could not achieve success in this expedition and was murdered by the rebels and the royal forces returned to Delhi without any positive gain. Although the death of Shadi Khan, the son-in-law of the Sultan, was a bolt from the blue for him, yet he did not give up royal policy of expansion, and decided to invade Bengal.
Conquest of Bengal:
Bengal had ever been a problem State for the Sultans of Delhi. After the death of Balban and accession of Kaiqubad, Bughra Khan, the second son of Balban, ruled over Bengal like an independent ruler. Alauddin Khalji, anyhow, established his rule over Bengal. Its ruler Shamsuddin Firoz Shah, a descendant of Bughra Khan, breathed his last in 1322 A.D. and left behind four sons for waging a war of succession.
In a fratricidal war Ghiasuddin Bahadur succeeded and he established his control over Bengal but he did not prove to be a successful ruler and resorted to the policy of oppression and exploitation, which annoyed the people. One of his brothers, Nasiruddin, requested Sultan Ghiasuddin for intervention and the Sultan of Delhi taking the advantage of the family feud intervened in the politics of Bengal.
He himself marched towards Bengal with a vast and powerful army and made his son incharge in Delhi for looking after the work of administration in his absence. Ghiasuddin Bahadur faced the joint force of the Sultan of Delhi and his brother Nasiruddin but was, ultimately defeated. He was imprisoned and sent to Delhi where he was treated very kindly. Nasiruddin was declared the ruler of Bengal. He accepted the supremacy of Delhi and promised to send annual tribute. Thus the authority of Sultan Ghiasuddin Tughluq was established in Bengal.
Conquest of Tirhut (Mithila):
While returning to Delhi from Bengal, Sultan Ghiasuddin invaded Hari Singh Deva of Tirhut who fought very bravely but was defeated. He fled away to the forests but was once again defeated and Tirhut was incorporated in Delhi Sultanate.
Death of Ghiasuddin Tughluq:
When Ghiasuddin was coming back to Delhi after the victory over Bengal and Tirhut, his son Juna Khan made a wooden palace at Afghanpur near Delhi for the welcome of his victorious father. A magnificent feast was arranged there.
After taking their meals when the guests went out of the palace to wash their hands, all of a sudden the wooden structure fell down and the Sultan was buried under it, along with his son Mahmood. Lanepoole writes, “On his return from his expeditions the gallant old Sultan met his death by fall of a roof which crushed him beneath its ruins.”