3 subfields of business that are of interest to me are listed below. Please list the major theories related to these topics. How might these theories be applied in the practice of business? Internet

3 subfields of business that are of interest to me are listed below.  Please list the major theories related to these topics. How might these theories be applied in the practice of business? 

Internet references only please for verification, thank you and nothing too long, just a few words about each subfield.

Leadership styles

Training and Development

Retention