The most significant event between the 7th and 11th century was the Tripartite struggle centered on Kannauj that lasted for more than two centuries between the Pala Empire, Rashtrakuta Empire, and Gurjara Pratihara Empire. Southern India was ruled by the Chalukya, Chola, Pallava, Chera, Pandyan, and Western Chalukya Empires. The seventh century also saw the advent of Islam as a political power, though as a fringe, in the western part of the subcontinent, in modern-day Pakistan. The Chola dynasty conquered southern India and successfully invaded parts of Southeast Asia, Sri Lanka, Maldives and Bengal in the 11th century. The early medieval period Indian mathematics influenced the development of mathematics and astronomy in the Arab world and the Hindu numerals were introduced.