Why did the cholas build a strong naval fleet?

The cholas built a strong naval fleet in order to show their strength and conquer the islands of Sri Lanka, Maldives and control the trade of those areas. During the reign of Rajendra Chola, Indian merchants were trading with various parts of South East Asia and Southern China, through the straits of Malacca, which was held by the kingdom of Shrivijaya. The merchants of Shrivijaya began creating problems for the Indian merchants. The Indian merchants appealed to Rajendra Chola for help. He sent out a huge Navy and defeated Shrivijaya king. As a result, Indian trade with South-East Asia and southern China continued, thereby enriching the Chola kingdom.