Complex sentence: Nearly all-early research on minority influence focused on how the majority influenced the minority, based on the assumption of many psychologists that it would be very hard for the minority to have any influence on the majority.
Split into simpler sentences: Nearly all-early research on minority influence concentrated on the way in which the majority influenced the minority. This was due to the assumption of many psychologists that it would be very hard for the minority to have any influence on the majority.