Reasons that remained Bengal problem for the Delhi Sultanate.

(i) Bengal was the easternmost province of Delhi Sultanate. Lack of proper means of transportation and communication created difficulty in controlling this province.

(ii) Though Bengal was annexed to Delhi Sultanate, a number of times it gained its independence. During the last decade of the 12 century AD Muhammad bin Bakhtiyar annexed Bengal to the conquered territories of Muhammad Ghori. But after his death, his successors declared their independence with the support of the local people.

(iii) Balban forced Bengal to accept the sovereignty of Delhi and appointed, his son Bughra Khan as its governor. But after Balban's death he declared his own independence.

(iv) Ghiyasuddin Tughlaq tried to solve this problem by partitioning Bengal into three independent administrative divisions namely Lakhnauti, Satgaon and Sonargaon.

(v) Muhammad bin Tughlaq tried to declare the supremacy of Delhi Sultanate but when he was busy suppressing rebellion in other parts of Sultanate, Bengal cut off its connection with Delhi.

(vi) Firoz Shah Tughlaq invaded Bengal and tried to capture it but Haji Iliyas, a noble who had united Bengal and had become its ruler, repulsed his attack. Tughlaq had to sign a treaty with Iliyas. According to the treaty, river Kosi was accepted as the boundary line between two kingdoms.