Conquests of Harshavardhana reveal that he had followed the policy of Digvijaya. He had ascended the throne of Thanesar in 606 A.D. His ascension to the throne was a period of political turmoil in Pushabhukti House, owing to the sudden death of Rajya Vardhana, elder brother of Harshavardhana, in the hands of Sasanka of Gauda. Harsha`s immediate task after his ascension to the throne was to avenge his enemies. Harsha Vardhana had first outlined the plan of "Digvijaya", which he readily pursued. Harsha and his feudatories dreamt to conquer distant lands, though campaign against Sasanka was his immediate target. After the conquest of Bengal and eastern India, Harsha Vardhana`s thirst for conquest increased considerably and he devoted himself to the scheme of conquering whole of India and accomplished successful takeovers for a long period of thirty years. The River Narmada was the southern boundary of Harsha`s kingdom.

The military campaigns and conquests of Harsha Vardhana can be categorised into several phases - conquest of Bengal and Eastern India, campaign against western India, the Chalukya War and his war with Sindh. On the northern frontier of his kingdom, Harsha came into contact with Kashmir. Chinese traveler HieunTsang has vividly mentioned some of the famous conquests of King Harsha Vardhana in his writings. Some of them are listed here.

Campaign in East India
The primary objective of Harsha`s campaign in East India was to defeat Sasanka and expand his dominion. According to historical accounts such as the “Harshacharita” and “Arya-manju-shri-mul-kalpa”, Harsha not only emerged victorious against Sasanka but also conquered several other smaller kingdoms that stood in his path to triumph. Following Sasanka`s demise, Harsha seized control of Gaud. Furthermore, Kamrupa in the east had already come under the influence of King Harsha, as Bhaskarvarman, the ruler of Kamrupa, had willingly accepted Harsha`s authority. Consequently, Harshavardhan`s eastward conquest resulted in forming friendship alliances with numerous kingdoms. The ruler of Magadha, Pundravarmana, also acknowledged Harsha`s supremacy, and even Nalanda, along with Magadha, embraced Harsha`s hegemony. A seal discovered from the region indicated that Ayodhya was under Harshavardhana`s rule. Additionally, Harsha organized the `Mahamoksha Parishad` in Prayag every five years. The novel Ratnawali also mentions the existence of Kosambhi bhukti.

The Battle of Vallabhi
Vallabhi, an empire situated in Gujarat, became the target of Harsha`s military campaign. Dhruvsena II, also known as Dhruv Bhatta, ruled over Vallabhi, and Harsha launched an attack against him, resulting in his defeat. Jay Bhatta III`s writings extensively describe this event. Both Harsha and the Chalukya dynasty had an interest in Vallabhi from a political standpoint. Consequently, Harsha formed a friendly alliance with Dhruvsena II and married his daughter, thereby securing his military forces along the western border. This move effectively limited the expansion of the Chalukyas into northern territories. This diplomatic success proved to be one of Harsha`s most notable achievements.

Campaign in Sindh
Sindh, situated adjacent to Harsha`s kingdom, presented an opportunity for territorial expansion. Banbhatta`s detailed account in the Harshacharita depicts how Harshavardhana treated the king of Sindh with great respect and honor while extracting substantial wealth from him. This war strategy employed by Harshavardhana aided in overcoming the Vardhana dynasty`s longstanding enemy, Sindh. However, Hieun-Tsang`s writings provide conflicting information, describing Sindh as an independent and powerful kingdom. Thus, the exact details of Harsha`s victory over Sindh remain uncertain.

Campaign in Bengal
After Sasanka`s death in 620 AD, Harshavardhana initiated a campaign to conquer a significant portion of Bengal. He achieved supremacy over Samtat, Tamralipti, Karnasuarna, and Pundravardhan. Following the conquest of Bengal, Harshavardhana issued a copper inscription known as the Daanpatra. According to an inscription from Bengal it is probable that the whole of Bengal passed under the rule of Harsha. The discovery of an inscription from Eastern Bengal dated in the Harsha era proves that the region was under the sway of the Kannauj monarch.

War against Chalukyas
Chalukya War of Harsha Vardhana had confined the area of Harsha`s sovereignty. Harsha with the aim of becoming the sole lord of India had projected his campaign against the southern kingdom. But he was confronted with the powerful resistance of Chalukya king Pulakesin II of Vatapi. Hence Harsha Vardhana could not extend the limits of his Empire to the south of the Narmada River. The Chalukya war of Harsha Vardhan destined him as the paramount ruler of north, who had no supremacy over the kingdoms of south India.

Conquests in Deccan India
According to Hieun-Tsang`s writings, Harshavardhana gained control over Jejakbhukti (Bundelk hand), Maneshwarpur (Gwalior), Gurjar, and Ujjain in the Deccan region.

Campaign of Kashmir and Nepal
The accounts of Banbhatta and Hieun-Tsang mention Harshavardhana`s alleged victories over Nepal and Kashmir. According to Hieun-Tsang, Harsha carried the tooth relic of Gautam Buddha from Kashmir to Kannauj and constructed a sangharam there. The prevalence of the Harsha Samvat calendar in Nepal implies that Nepal was under Harshavardhana`s control.

Campaign in Odisha
By 640 AD, Harshavardhana had brought northern and southern parts of Odisha and Kalinga under his dominion. With this triumph, Harshavardhana extended his control over the entire northern India. Consequently, he adopted the title of Shaklotarapathnath. Having consolidated his empire, Harsha implemented his imperialist policies, leading many to consider him the establisher of a vast and unified empire after the Gupta dynasty.

Expansion of Empire by Harshavardhana
Harshavardhana inherited the territories of Delhi, Thaneshwar, and eastern Punjab. While his father, Prabhakar Vardhana, had won a few battles, he had been unable to expand the kingdom`s boundaries. Harsha added Kannauj, extending the boundary of his empire northwards. The Banskheda and Madhuban copper plates reveal that Ahichatra and Shravasti were also part of his empire. Another account states that Harsha assumed the title of Magadhadhiraj in 641 AD, indicating the annexation of Magadha. Hieun-Tsang describes how Munger district was also conquered by Harsha and subsequently donated to Buddhist monks. Moreover, Harshavardhana is said to have annexed Odra (Odisha) and Kongodh (present-day Ganjam), as supported by the donation of 80 villages in Odisha to Buddhist monks, which the monks later refused.

In the south, the boundaries of Harsha`s empire extended up to the Narmada River, beyond which the Chalukyan kingdom began. Additionally, some portions of Vallabhi remained outside Harshavardhana`s control, making it unclear whether he had complete dominion over Gujarat and Saurashtra. However, western Malwa was firmly under Harshavardhana`s rule. While he may have achieved victory over Sindh, he did not incorporate it into his empire. The ruler of Sindh acknowledged Harshavardhana`s supremacy while maintaining his independence. The ruler of Kamrupa, Bhaskarvarman, willingly accepted Harshavardhana`s authority, though it is debated whether this relationship was solely a result of their common enemy, Sasanka, the ruler of Gaud. Bhaskarvarman attended the Mahamokshaparishada as a friend of Harsha rather than as a subordinate ruler.

Harshavardhana`s campaigns in East India, including his victory over Sasanka and the subsequent annexation of various kingdoms, showcased his military prowess and strategic acumen. His diplomatic endeavors, such as forging alliances with rulers like Dhruvsena II of Vallabhi and maintaining cordial relations with neighboring territories, allowed him to extend his influence and establish a vast empire. Harsha`s rule spanned from Assam to Kashmir and from Himachal to Vindhyachal, making him a prominent ruler in northern India.

Harshavardhana also maintained friendly relations with the ruler of Kashmir, Durlabha Vardhana. According to Hiuen-Tsang`s biography, the ruler willingly presented Harshavardhana with the tooth relic of Lord Buddha, signifying their amicable bond. Thus, it can be inferred that the ruler of Kashmir sought to maintain cordial relations with Harsha.

It is important to note that Harsha did not exercise direct control over all the territories under his influence. Instead, he exerted his authority and influence over these regions through alliances, vassalage, and friendly relations with local rulers. His ability to establish diplomatic ties and secure the support of neighboring kingdoms played a crucial role in expanding his influence. Harshavardhana`s conquests and the establishment of his empire marked a significant chapter in Indian history. He not only expanded his territorial boundaries but also sought to promote cultural and intellectual advancements.