Early in the Medieval era, Kedah became part of Srivijaya (the dominant Malay state and a major power in the Indian Ocean trade). This led to rivalries with the Indian states, especially the Chola Empire from the 9th to 13th centuries CE. The Cholas had a powerful merchant and naval fleet in the Indian Ocean and the Bay of Bengal. In the early 11th century, Tamil Chola King Rajendra Chola I sent an expedition to attack Kedah (Sri Vijaya) on behalf of one of its rulers who sought his assistance to gain the throne.