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.

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.

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.