Osaka is the largest city in western Japan. The 16th-century warlord Toyotomi Hideyoshi, who unified Japan after a long period of civil war, chose it as his power base and built a castle there to serve as the power base for his clan. In the years that followed, Osaka became a major logistical and economic hub. From the mid-19th century, Osaka rode the wave of Japan's modernization and the city expanded rapidly. The development of its spinning industry brought prosperity. During this period it was known as "Great Osaka" and saw the construction of many handsome commercial buildings, several of which survive to this day. From the late 1940's, the city was a driving force for Japan's postwar reconstruction and rapid economic growth. In 1970 it became the first city in Asia to host a world's fair, known as Expo '70. On this episode of Journeys in Japan, American architect James Lambiasi visits Osaka and explores its history and culture, as reflected in its impressive architecture.