Sociologist Saskia Sassen's work, especially her seminal 1991 book The Global City: New York, London, Tokyo, is largely responsible for the idea of global cities.Although "world cities" were discussed prior to Sassen, her concept concentrated on how cities were changing as a result of globalization. She maintained that as the global economy grew more interconnected, some cities became essential centers for the following reasons:International FinanceParticularized ServicesControl and ManagementImportant Points:The primary source is Saskia Sassen's work from the early 1990s.Focuses on how cities affect the world economy.Draws attention to their significance in corporate control, specialized services, and finance.These cities are part of a global network that is interconnected.Two major forces are globalization and the growth of multinational firms.