<P> The mountainous Japanese archipelago stretches northeast to southwest 3,000 km off the east of the Asian continent at the convergence of four tectonic plates; it has about forty active volcanoes and experiences about 1,000 earthquakes a year . The steep, craggy mountains that cover two - thirds of its surface are prone to quick erosion from fast - flowing rivers and to mudslides . They thus have hampered internal travel and communication and driven the population to rely on transportation along coastal waters . There is a great variety to its regions' geographical features and weather patterns, with a rainy season in most parts in early summer . Volcanic soil that washes along the 13% of the area that makes up the coastal plains provides fertile land, and the mainly temperate climate allows long growing seasons, which with the diversity of flora and fauna provide rich resources able to support the density of the population . </P> <P> A commonly accepted periodization of Japanese history: </P> <Table> <Tr> <Th> Dates </Th> <Th> Period </Th> <Th> Period </Th> <Th> Subperiod </Th> <Th> Main government </Th> </Tr> <Tr> <Td> 30,000--10,000 BC </Td> <Td_colspan="2"> Japanese Paleolithic </Td> <Td> </Td> <Td> unknown </Td> </Tr> <Tr> <Td> 10,000--300 BC </Td> <Td> Ancient Japan </Td> <Td> Jōmon </Td> <Td> </Td> </Tr> <Tr> <Td> 300 BC--300 AD </Td> <Td> Yayoi </Td> <Td> </Td> </Tr> <Tr> <Td> 300--538 </Td> <Td> Kofun </Td> <Td> </Td> <Td> Imperial government </Td> </Tr> <Tr> <Td> 538--710 </Td> <Td> Classical Japan </Td> <Td> Asuka </Td> <Td> </Td> </Tr> <Tr> <Td> 710--794 </Td> <Td> Nara </Td> <Td> </Td> </Tr> <Tr> <Td> 794--1185 </Td> <Td> Heian </Td> <Td> </Td> </Tr> <Tr> <Td> 1185--1333 </Td> <Td> Medieval Japan </Td> <Td> Kamakura </Td> <Td> </Td> <Td> Kamakura shogunate </Td> </Tr> <Tr> <Td> 1333--1336 </Td> <Td> Kenmu Restoration </Td> <Td> </Td> <Td> Imperial government </Td> </Tr> <Tr> <Td> 1336--1392 </Td> <Td> Muromachi </Td> <Td> Nanboku - chō period </Td> <Td> Ashikaga shogunate </Td> </Tr> <Tr> <Td> 1392--1467 </Td> <Td> </Td> </Tr> <Tr> <Td> 1467--1573 </Td> <Td> Sengoku period </Td> <Td> Ashikaga shogunate and sengoku daimyōs </Td> </Tr> <Tr> <Td> 1573--1603 </Td> <Td> Azuchi--Momoyama </Td> <Td> Oda Nobunaga, Toyotomi Hideyoshi and Tokugawa Ieyasu </Td> </Tr> <Tr> <Td> 1603--1868 </Td> <Td> Early Modern Japan </Td> <Td> Edo </Td> <Td> Tokugawa period </Td> <Td> Tokugawa shogunate </Td> </Tr> <Tr> <Td> 1868--1912 </Td> <Td> Modern Japan </Td> <Td> Meiji </Td> <Td> Pre-war </Td> <Td> Imperial government </Td> </Tr> <Tr> <Td> 1912--1926 </Td> <Td> Taishō </Td> </Tr> <Tr> <Td> 1926--1945 </Td> <Td> Shōwa (Prewar) </Td> </Tr> <Tr> <Td> 1945--1952 </Td> <Td> Contemporary Japan </Td> <Td> Shōwa (Occupied Post-war) </Td> <Td> Post-war </Td> <Td> GHQ / SCAP </Td> </Tr> <Tr> <Td> 1952--1989 </Td> <Td> Shōwa (Post-occupation) </Td> <Td> Parliamentary democracy </Td> </Tr> <Tr> <Td> 1989--present </Td> <Td> Heisei </Td> </Tr> </Table> <Tr> <Th> Dates </Th> <Th> Period </Th> <Th> Period </Th> <Th> Subperiod </Th> <Th> Main government </Th> </Tr>

Who was the ruling figurehead of japan during the medieval time period
find me the text answering this question