Coming to the throne at a critical time when enemies were active, Harsha Siladitya immediately decided upon a course of adventure and aggression.
He thought of wars and conquests as the mission of his political career. With the help of his army chief, he prepared a plan for his digvijaya to punish the King of Gauda and other enemy kings.
He directed his War Minister to demand from the neighbouring kings their immediate homage to him.
While preparing for extensive wars, Harsha thought it his first urgent duty to rescue his sister, Rajyasri. The Chief Minister Bhandi brought the news that Rajyasri, soon after she was thrown into prison in Kanauj managed to escape from her confinement and had gone away towards the Vindhya forests. Harsha forthwith proceeded towards the Vindhyas in search of his sister. The forest-chiefs of those wild regions as well as some monks helped him in that difficult task. Rajyasri was finally traced and rescued when she was about to throw herself into fire and die. With that noble work done, Harsha was free to conduct his military campaigns.
India at the accession of Harsha presented a fertile ground for the rise of a strong monarchy. For more than a century after the fall of the Guptas, India passed through a phase of political disruption. The ideal of a Chakravarti King had almost been forgotten when no king could rise to the occasion to take up a digvijaya to subdue the smaller kings. Harsha possessed the heroic qualities of a warrior to take up that lost legacy of the Mauryas and the Guptas. Though very young, he was brave and ambitious enough to start his campaigns to bring a vast area of India under one imperial umbrella.
From the descriptions of Bana it is known that Harsha carried his campaigns with an army of 5000 elephants, 20,000 horses and 50,000 infantry. According to Hiuen Tsang, Harsha “went from east to west sub-during all who were not obedient; the elephants were not unharnessed nor the soldiers un-helmeted.” It is further understood from his accounts that in six years of his incessant warfare Harsha brought “the Five Indies under his allegiance,” and became the Lord Paramount of the North. Some historians believe that the ‘Five Indies’ refer to Saurashtra, Kanauj, Gauda or Bengal, Mithila, and perhaps a part of Orissa. His wars did not end in those six years only. Evidences show that he was fighting wars till the very end of his reign which covered a period of forty-two years.
During his vigorous wars of conquests, Harsha met with only one check in his military advance. In 620 A.D., when he directed his armies towards the south to conquer the Deccan, he was checked by the powerful Chalukya King, Pulakesin II, who claimed himself as the Paramount Lord of the South. Though there is no doubt that Harsha brought most of northern India under his rule, his exact conquests of different territories were not clearly stated either by Baha or by Hiuen Tsang. The following of his conquests, however, can be ascertained from their descriptions, as also from other evidences.
Bana gives a description of Harsha’s military preparations against his worst foe, King Sasanka of Gauda or Bengal. Both Bana and Hiuen Tsang describe Sasanka as a bad king. It is understood that Harsha’s campaigns against him continued for a number of years. In his first campaign, as is gathered from the Manjusri-Mulakalpa, Harsha invaded Pundra, the capital of Sasanka, defeated him, and ordered him not to come out of his country. It is after Sasanka’s death after some years, that Harsha annexed his territories of Bengal and South Bihar, including Magadha, to his empire.
A part of Bengal and Assam, passing under the name Kamarupa, was ruled by King Bhaskara-Varman who was an ally of Harsha, and therefore, an enemy of Sasanka. He acknowledged the suzerainty of Harsha and remained loyal to him. In eastern India, thus, Harsha’s authority was established over Magadha, Bengal and Assam.
In the west, Sindh was conquered by Harsha. According to Bana, Harsha “pounded the King of Sindhu and appropriated his fortune.” In western India, Harsha also invaded and conquered the kingdom of Vallabhi ruled by King Dhruvasena II Baladitya. This King accepted the authority of Harsha as his over-lord. Harsha, too, gave his daughter in marriage to him. Dhruvasena was permitted to rule as a subordinate chief under the emperor.
Harsha’s authority was also established over the neighbourhood states of Vallabhi, namely Kutch, Saurashtra or Southern Kathiawar, and western Malwa.
In the extreme north, Harsha’s empire extended to “an inaccessible land of snowy mountains”, as described by Bana. To some historians, this land was Nepal, because the Harsha Era was in use in that territory as is seen in the Nepalese inscriptions. According to some others, the ‘land of snowy mountains’ was Kashmir.
This suggestion is made because of an account contained in the Life of Hiuen Tsang. According to that account Harsha compelled the King of Kashmir to part with a relic of Buddha. It might be that either Nepal or Kashmir, or both, had come under the suzerainty of Harsha.
In the south-eastern India, Harsha’s conquest of Orissa, or a part of Orissa, is established from the accounts of Hiuen Tsang. Kongoda or the Ganjam region of Orissa is said to be the last of the conquests of Harsha. It was achieved in 643 A.D., only four years before Harsha’s death. It is understood that after his expeditions to Kongoda, Harsha camped in Orissa and held a conference of the Mahayana Buddhists. To that conference were invited the Buddhist scholars from Nalanda. After the debates and discourses in that conference, Harsha offered to a Buddhist scholar of Orissa named Jayasena “the revenue of eighty large towns of Orissa.”
While Harsha achieved success in all quarters of India, he suffered a reverse while invading the south. The powerful Chalukya King Pulakesin II opposed his aggression into the Deccan. It is gathered from the Life of Hiuen Tsang, written by a friend of that celebrated pilgrim, that “Siladitya Raja boasting of his skill, and the invariable success of his generals, filled with confidence, himself marched at the head of his troops to contend with this prince but he was unable to prevail or subjugate him (Pulakesin II), although he has gathered troops from the ‘Five Indies’ and the best generals from all countries.”
Harsha’s failure to conquer the Deccan is also known from the Aihole Inscription of A.D. 634 of the poet Ravikirti. The inscription describes the battle stating that Harsha “had his joy melted away by fear, with his rows of lordly elephants fallen in battles.”
The inscription also gives an indication of the place of battle between Pulakesin and Harsha somewhere between the Vindhyas and the Narmada. Harsha is described in the Chalukya records as the Sakala-Uttarapatha-natha or the Lord of the whole of Uttarapatha. Thus that Harsha’s ambition to bring the south under his northern empire ended without success. On the other hand, his supremacy over the north was recognised in the south.