Meanwhile, attracted to the mild Mediterranean climate, cheap land, and the state's wide variety of geography, filmmakers established the studio system in Hollywood in the 1920s. California manufactured 8. 7 percent of total United States military armaments produced during World War II, ranking third (behind New York and Michigan) among the 48 states.  California however easily ranked first in production of military ships during the war (transport, cargo, [merchant ships] such as Liberty ships, Victory ships, and warships) at drydock facilities in San Diego, Los Angeles, and the San Francisco Bay Area.  After World War II, California's economy greatly expanded due to strong aerospace and defense industries, whose size decreased following the end of the Cold War. Stanford University and its Dean of Engineering Frederick Terman began encouraging faculty and graduates to stay in California instead of leaving the state, and develop a high-tech region in the area now known as Silicon Valley.  As a result of these efforts, California is regarded as a world center of the entertainment and music industries, of technology, engineering, and the aerospace industry, and as the United States center of agricultural production.  Just before the Dot Com Bust, California had the fifth-largest economy in the world among nations.  Yet since 1991, and starting in the late 1980s in Southern California, California has seen a net loss of domestic migrants in most years. This is often referred to by the media as the California exodus.