During the 1980s and 1990s, Sassen emerged as a prolific author in urban sociology. She studied the impacts of globalisation such as economic restructuring, and how the movements of labour and capital influence urban life. She also studied the influence of communication technology on governance. Sassen observed how nation states begin to lose power to control these developments, and she studied increasing general transnationalism, including transnational human migration. She identified and described the phenomenon of the "global city". Her 1991 book bearing this title made her a widely quoted author on globalisation. An updated edition of her book was published in 2001. In the early 2000s, Sassen focused on immigration and globalization, with her "denationalization" and "transnationalism" projects (see Bibliography and External Links, below). Her books have been translated into 21 languages.