Complex sentence: As an African American, Sumner faced significant hindrances to his advancement as a psychologist.The early 20th Century was a time of exploration and research into the elucidation of race based mythology regarding the innate inferiority of non-European peoples.
Split into simpler sentences: As an African American, Sumner faced significant hindrances to his advancement as a psychologist. Regarding race relations, the early 20th Century was a time of exploration and research into the elucidation of race based mythology regarding the innate inferiority of non-European peoples.