Massive and parallel changes have occurred in New York City since the late 1970s and in London and Tokyo since the early 1980s. What transformed these urban centers, with their diverse histories, into "global cities" that share comparable economic and social structures? Saskia Sassen argues that their remarkable similarity arises from their position as command posts in international finance and advanced services for business. Massive and parallel changes have occurred in New York City since the late 1970s and in London and Tokyo since the early 1980s. What transformed these urban centers, with their diverse histories, into "global cities" that share comparable economic and social structures? Saskia Sassen argues that their remarkable similarity arises from their position as command posts in international finance and advanced services for business.