The decline of the Gupta Empire was followed by a period of political disorder and disunity in North India. It was only in the beginning of the seventh century A.D. that Harshvardhana succeeded in establishing a larger kingdom in north India.
The chief sources for tracing the history of Harsha and his times are the Harshacharita written by Bana and the Travel accounts of Hiuen Tsang. Bana was the court poet of Harsha. Hiuen Tsang was the Chinese traveler who visited India in the seventh century A.D. Besides these two sources, the dramas written by Harsha, namely Ratnavali, Nagananda and Priyardarsika also provide useful information. The Madhuben plate inscription and the Sonpat inscription are also helpful to know the chronology of Harsha. The Banskhera inscription contains the signature of Harsha.
In his first expedition, Harsha drove out Sasanka from Kanauj. He made Kanauj his new capital. This made him the most powerful ruler of north India. Harsha fought against Dhuruvasena II of Valabhi and defeated him. Dhuruvasena II became a vassal.
The most important military campaign of Harsha was against the Western Chalukya ruler Pulakesin II. Both the accounts of Hiuen Tsang and the inscriptions of Pulakesin II provide the details of this campaign. Harsha with an ambition to extend his kingdom south of the Narmada river marched against the Chalukya ruler. But the Aihole inscription of Pulakesin II mentions the defeat of Harsha by Pulakesin, who after this achievement assumed the title Paramesvara. Hiuen Tsang's accounts also confirm the victory ofPulakesin.
Harsha led another campaign against the ruler of Sindh, which was an independent kingdom. But, it is doubtful whether his Sind campaign was a successful one. Nepal had accepted Harsha's overlordship. Harsha established his control over Kashmir and its ruler sent tributes to him. He also maintained cordial relations with Bhaskaravarman, the ruler of Assam. Harsha's last military campaign was against the kingdom of Kalinga in Orissa and it was a success.
Thus Harsha established his hold over the whole of north India. The regions modern Rajasthan, Punjab, Uttar Pradesh, Bihar and Orissa were under his direct control. But his sphere of influence was much more extensive. The peripheral states such as Kashmir, Sind, Valabhi and Kamarupa acknowledged his sovereignty.