At the instance of Kṛṣṇa, Arjuna, performed the severe penance of Śiva and obtained a divne missile duo to Śiva’s boon. He then conquered the Kauravas.
विनाश्य पाण्डवसुताञ्छिक्षितानपि यत्नतः ।। कृष्णादिभिर्महावीरैरनिवार्य्यबलः परैः ।। २० ।।
He destroyed the sons of Pāṇḍavas though they were trained in warfare by Kṛṣṇa and other great heroes. He had the strength that could not be withstood bv the enemy.