The Kohun Period started at the end of the 3rd century. Characteristics of this period are the introduction of Chinese characters, the appearance of huge tumuli, the unification of Japan by the Yamato Court, an inflow of foreign visitors, new skills and knowledge imported from China and Korea, the introduction of iron farm tools and weapons throughout Japan, and the introduction of Buddhism. By the end of the 4th century, Japan went to war against Korea. About the same time, Japan established a government office in Korea. This government office only lasted until the middle of the 6th century. Although Chinese characters were introduced, these characters were usually limited to commerce between China, Korea, and Japan. Therefore, archaeologists and historians sometimes refer to the Chinese historical record in order to understand Japanese history for the Kohun Period. This Kohun Period is followed by Asuka period which started in the middle of 6th century.