His objective was to eliminate the surviving family members of his predecessor Jalaluddin Khalji, whom he had assassinated to usurp the throne of Delhi.
Multan, which was located in the Punjab region to the north-west of Delhi, was under the control of Jalaluddin's eldest son Arkali Khan.
[1] Jalaluddin's widow (the former queen or Malka-i-Jahan) and his younger son Ruknuddin Ibrahim had taken shelter in Multan after fleeing Delhi.
After strengthening his control over Delhi, Alauddin decided to conquer Multan and eliminate the surviving family of Jalaluddin.
[2] Alauddin himself did not lead an expedition to Multan, as it was important for him to remain in Delhi to keep control of the recently-gained throne.
However, after two months of being besieged, his kotwal (fort commander) and some leading citizens were convinced that Alauddin's forces would ultimately emerge victorious.