For at least 120 years, (630-750) during the Tang dynasty China was the largest and strongest country on earth. At this time, the Central Kingdom was an open forum, a world market of ideas, people, and things. The capital was cosmopolitan; trade and foreign visitors were encouraged. The Tang empire was at its peak and the emperor was known as the "Heavenly Khan" to all neighbors in East, Central and South Asia. Satellite kingdoms were situated in and around Samarkand, Tashkent, Kashmir, Afghanistan and Persia. The Tang court sent military governors as far west as Teheran while garrisons along the East-West land link facilitated the flow of goods and people. At the same time, much trade with Persians and Arabs was conducted through sea routes. In the south, China traded with India and countries surrounding the subcontinent and received envoys from Nepal, Burma and islands in the South Seas as far as Java and Sumatra. A native Korean kingdom repulsed Japanese advances and united the peninsula with Tang assistance. Sinicization of Japan, begun during the Han dynasty, reached its apex during Tang. Tolerant toward all religions, the Tang court protected the Nestorian Christian faith which came to China in the 7th century. The Islamic religion also penetrated China during Tang, becoming dominant in the northwest; and during the period Buddhism developed into several major schools.