Critical theory is an expression typically used to refer to the circle of philosophers and social scientists that had its beginning in Frankfurt, Germany in the 1920s. Known as the Frankfurt School, they aimed to unite Marxist theory and social scientific research in order to respond to social and political issues of the time. Initially concerned with critically evaluating a tendency towards totalitariansm in western society, which they attributed to the power of capitalism, they extended their critique to include science and technology and the instrumental conception of reason associated with them. The three most important philosophers associated with the Frankfurt School were Max Horkheimer, Theodor Adorno and Herbert Marcuse. The Institute for Social Research, which they established to carry out their aims, was moved to New York in 1933 when the National Socialists came to power in Germany. As a result, much of the important work of the Frankfurt School was done in exile. After the War, the Institute returned to Frankfurt, but Marcuse remained in the United States where he taught at several American universities. Significant differences emerged among the original members of the Frankfurt School and critical theory sometimes refers broadly to any critical theory that focuses on systematic analyses of the causes and forms of social and political oppression, and the emancipation of persons for a better life.