Having deceived him on the way by present. Duryodhana induced him to grant him a boon and for that boon he asked his help in the war.
उपहारैर्वञ्चयित्वा वर्मन्येव सुयोधनः। वरदं तं वरं वत्रे साहाय्यं क्रियतां मम॥