Final answer:
Emerson’s main concern was individuality and the spiritual connection to nature. He defined a great man as a nonconformist who is true to his own beliefs.
Step-by-step explanation:
Ralph Waldo Emerson's main concern was the need for individuality and spiritual connection with nature, as opposed to the conformity and societal pressure seen in the rapidly industrializing America. A great man, according to Emerson, is a nonconformist, one who is true to themselves and their own convictions rather than following the crowd. This view is especially emphasized in his essay "Self-Reliance", where he implores people to think independently and resist societal conformities.