Complex sentence: By the early 1890's chicago had become a major centre for New Thought, mainly throught the work of Emma Curtis Hopkins, and Atkinson decided to move there and he became an active promoter of the movement as an editor and author.
Split into simpler sentences: By the early 1890's Chicago had become a major centre for New Thought, mainly through the work of Emma Curtis Hopkins, and Atkinson decided to move there. Once in the city, he became an active promoter of the movement as an editor and author.