The Tripartite Struggle for control of northern India took place in the ninth century. The struggle was between the Gurjara-Pratihara Empire, the Pala Empire and the Rashtrakuta Empire. Towards the end of the successor of Nagabhata II,the ruler of pratiharas successfully attacked Kanauj and established control there.

Answer is d because these these dynasty are very powerful and they want kannauj. Because according to economic conditions kannauj is very important place at that time.

The correct answer is option 'D' - Gurjara-Pratihara, Rashtrakuta and Pala dynasties.

Explanation:
The tripartite struggles were a series of conflicts that occurred during the 8th to 10th centuries in India. These struggles involved three major dynasties - the Gurjara-Pratihara, Rashtrakuta, and Pala dynasties.

1. Gurjara-Pratihara Dynasty:
- The Gurjara-Pratihara Dynasty was a powerful dynasty that ruled over a large part of northern India from the 6th to the 11th centuries.
- They were of Rajput origin and their capital was Kannauj.
- The Gurjara-Pratiharas played a significant role in Indian history and were known for their military prowess.

2. Rashtrakuta Dynasty:
- The Rashtrakuta Dynasty was an imperial power that ruled over a large part of the Deccan region from the 8th to the 10th centuries.
- They were of Kannada origin and their capital was Manyakheta (present-day Malkhed in Karnataka).
- The Rashtrakutas were known for their patronage of art and literature, as well as their military campaigns.

3. Pala Dynasty:
- The Pala Dynasty was a Buddhist dynasty that ruled over the Bengal region from the 8th to the 12th centuries.
- They were of Bengali origin and their capital was Pataliputra (present-day Patna in Bihar).
- The Palas were known for their patronage of Buddhism, as well as their contributions to art, literature, and education.

Tripartite Struggles:
- The tripartite struggles refer to the series of conflicts that occurred between the Gurjara-Pratiharas, Rashtrakutas, and Palas for control over the fertile Gangetic plains.
- These struggles were primarily driven by a quest for political dominance and control over trade routes.
- The conflicts involved a series of military campaigns, alliances, and counter-alliances between the three dynasties.
- The battles were often fierce and resulted in significant territorial gains and losses for each dynasty.
- The tripartite struggles ultimately weakened all three dynasties and contributed to the decline of their respective empires.

In conclusion, the tripartite struggles involved the Gurjara-Pratihara, Rashtrakuta, and Pala dynasties. These conflicts played a significant role in shaping the political landscape of medieval India and contributed to the decline of these powerful dynasties.