How did Adorno discover authoritarian personality theory?
He was trying to figure out a way as to why nobody really stood up to Hitler. Especially since he would have had many advisers in the army who could have told him not to do it etc.
Adorno then conducted his study on ex-nazi soldiers then living in the USA. By using the f-scale he measured how fascist they were and once he had seen a pattern and came up with the personality type.
You can do the F-scale test too: http://personality-testing.info/tests/RWAS/