Making sense of the pastime of Dhruva Maharaja fighting the Yakṣas
The Yakṣas and Rākṣasas are the supernatural followers of Kuvera, who inhabit Alakāpurī and are present in the whole region of the higher-dimensional Himalaya mountains of Jambūdvīpa.
After Dhruva Maharaja returned from the forest, having achieved success in his austerities and being blessed by the Lord, he quickly ascended to the throne for his rule of 36,000 years, as predicted by the Lord.
Maharaja Uttānapāda left for the forest before organizing the marriage of Dhruva. He thought that achieving self-realization was more urgent than taking care of such family matters. Prabhupāda mentions in his purport to text one that Dhruva was still five years old when he was installed in the throne. Despite being a child he was perfectly qualified for the post. Since he had already received all transcendental knowledge from the Lord and achieved perfection, there was no need for him to go to the gurukula. Despite having been attached to Suruci, Uttānapāda was a saintly king, and his ultimate goal was self-realization. Different from ordinary materialists, who want to cling to power until their last breath, Rājarṣis like Uttānapāda rule out of duty and are anxious to leave to dedicate themselves to self-realization as soon as a qualified son is present.
Even though Dhruva was a pure devotee at this point, ruling a kingdom demands having a wife since the duties of a king include not only begetting children to continue his lineage but performing many different types of sacrifices where the wife should be present, apart from other duties. As an exemplary king, Dhruva fulfilled perfectly all these duties, by later marrying two qualified ladies from respectable lineages and begetting four children. Nowadays, if a man thinks about having more than one wife, he will do so with the idea of enjoyment, but in previous eras, qualified men would often marry more than one wife to beget more qualified children.
Uttama, the half-brother of Dhruva, didn't inherit the throne as his mother desired, but he was living comfortably in the palace, performing his duties as a Kṣatriya. Once, he went on a hunting excursion to the north and was killed by a powerful Yakṣa in the Himālaya Mountains. Suruci went in search of her son when he didn't return, and perished in a forest fire, just as predicted by the Lord. This didn't happen due to divine interference, but simply due to the results of her own actions. The Lord simply predicted it when He met Dhruva.
Dhruva and his brother lived in Bhārata-varṣa, in the southern part of Jambūdvīpa, the central island of Bhu-mandala. Nowadays, often the Indian subcontinent is referred to as "Bhārata-varṣa", but in the higher dimensional Bhu-mandala, Bhārata-varṣa is a much larger structure, which in connected to the other portions of Jambūdvīpa. This structure somehow is represented in the gross dimension as our spherical planet, but it is not exactly the same, just as a two-dimensional projection of a three-dimensional object is not exactly the same as the original object being represented.
There is a large chain of mountains in the center of Jambūdvīpa, just like the Himalayas are the center of the South Asian region, but the Himālaya Mountains in the central part of Jambūdvīpa are much larger and include other features not present in our planet, such as Mount Sumeru. It's difficult to conclude how these features of Bhu-mandala are represented in our gross dimension, but this is ultimately a futile exercise since even if they are present as part of other planets of our galaxy, we would not be able to go there by mechanical means.
Alakāpurī, in turn, is the capital of Kuvera, which is surrounded by beautiful gardens and lakes. The Mahabharata describes that the Pandavas visited the place during their exile, while Arjuna visited the celestial planets to collect weapons. Alakāpurī is situated in the northern part of Jambūdvīpa, north of Mount Sumeru, close to Mount Kailāsa, the abode of Lord Śiva.
The Yakṣas and Rākṣasas are the supernatural followers of Kuvera, who inhabit Alakāpurī and are present in the whole region of the higher-dimensional Himalaya mountains of Jambūdvīpa. Srila Prabhupada also connects them to Himālayan tribes like the Tibetans. Uttama was killed by the Yakṣas and this was a challenge to the authority of the king. Dhruva had authority over the whole Bhu-mandala, and killing his brother was a serious challenge to his rule, therefore it was his duty to avenge his brother and restore order. Dhruva took thus his chariot and weapons and went north to the Himalayas to meet the challenge. A great battle ensued, where both Dhruva and the Yakṣas employed different types of mystical weapons. Kuvera is the treasurer of the demigods, and his abode is extremely opulent. The soldiers were also richly ornamented with earrings, turbans, golden bracelets, armlets, etc.
The army of the Yakṣas was 130,000 strong, and jointly they shot so many arrows and other weapons around Dhruva that they covered Dhruva with an incessant shower of weapons, just like a mountain covered by rain. For a moment, the Yakṣas thought they had won, but quickly Dhruva's chariot emerged, just as the sun appearing from the fog. From this point, Dhruva regained the initiative and used his bow to cut through their army.
Dhruva conquered them using his bow, killing many soldiers and making the rest flee. However, using their power of illusion, Yakṣas created then terrible illusions, with dead bodies falling from the sky, dangerous animals coming to devour him, etc. These illusions presented a great challenge, and even Dhruva became perplexed for a short time, just as we may become perplexed when facing difficulties.
Great sages, however, quickly approached Dhruva and instructed him to surpass all illusions by the power of chanting the holy name, which is non-different from the Lord Himself. By chanting the holy names we directly associate with the Lord, who is the only true shelter. We surely face many difficult and dangerous situations during life, but our connection with the Lord established through the chanting of the holy names can make us surpass all of them. The sages who came to Dhruva were inspired by the Lord inside the heart to do so, and this also emphasizes the power of sādhu-saṅga, which can save us in the most dangerous moments.
Hearing the advice of the sages, Dhruva became again resolute. He prepared to use the nārāyaṇāstra, a specific arrow made by Lord Nārāyaṇa Ṛṣi Himself. As the norm for using a mystic weapon, he touched the water used for purification before invoking the astra.
There is no direct description in the Srimad Bhāgavatam about him obtaining this weapon, but on verse 4.11.3 Prabhupada translates the words ārṣa-astram (the weapon of the great sages) as "the weapon given by Nārāyaṇa Ṛṣi" and on his purport to verse 4.11.1, he mentions that "Dhruva Mahārāja was given a specific arrow made by Lord Nārāyaṇa Himself".
Nārāyaṇa Ṛṣi is the direct incarnation of the Lord, and by the context of the verses and the description by Srila Prabhupada, it appears that Lord Nārāyaṇa Ṛṣi was amongst the sages who instructed Dhruva Maharaja and that He personally delivered the nārāyaṇāstra to him in the battlefield. This weapon could be invoked by Dhruva Maharaja by chanting the holy name of the Lord. In this way, the chanting of the holy name by Dhruva became not just the source of purification and spiritual strength, but also a weapon that could defeat his enemies.
Just as we can instantly dispel all ignorance by chanting the holy names in full faith, Dhruva was able to easily dispel the illusions created by the Yakṣas by using the weapon of Lord Vishnu:
"Even as Dhruva Mahārāja fixed the weapon made by Nārāyaṇa Ṛṣi onto his bow, arrows with golden shafts and feathers like the wings of a swan flew out from it. They entered the enemy soldiers with a great hissing sound, just as peacocks enter a forest with tumultuous crowing.
Those sharp arrows dismayed the enemy soldiers, who became almost unconscious, but various Yakṣas on the battlefield, in a rage against Dhruva Mahārāja, somehow or other collected their weapons and attacked. Just as serpents agitated by Garuḍa rush towards Garuḍa with upraised hoods, all the Yakṣa soldiers prepared to overcome Dhruva Mahārāja with their upraised weapons." (SB 4.11.3-4)
Some of the soldiers somehow survived the attack of the nārāyaṇāstra and came forward in a last-ditch attempt to overcome Dhruva Maharaja, who quickly dispatched them using his arrows. Because Dhruva was such a great devotee, however, all the Yakṣas killed by him were immediately purified and elevated to Brahmaloka, achieving the same result as perfect brahmacārīs. Prabhupada mentions that killing performed by the Lord, his pure devotees, or in sacrifices awards great benefit. Animals killed in Vedic sacrifices achieve a human body, demons killed by the Lord attain liberation, and enemies killed by pure devotees of the Lord are also purified.
The attack of Dhruva against the Yakṣas of Alakāpurī happened due to valid reasons. It was his duty as the king to maintain order. It was his duty to punish the assassin of his brother, and since the Yakṣas offered resistance, it became his duty to pacify them. However, the battle went a little too far, with Dhruva almost exterminating the whole race due to the stubborn resistance of the Yakṣa warriors.
Seeing the scene, Svāyambhuva Manu became compassionate and came forward to pacify Dhruva, accompanied by great sages. This led Dhruva to stop the fighting and meet with Kuvera, the Lord of the Yakṣas, who was happy to meet such a great devotee and blessed him.