 The properties were mostly in Harlem and the Lower East Side, were decrepit and poorly maintained, and represented the largest concentration of real estate in those areas under the control of a single group.
<fluency>  The properties were mostly in Harlem and the Lower East Side, were decrepit and poorly maintained, and represented the largest concentration of real estate in those areas under the control of a single group.
 The properties , mostly in Harlem and the Lower East Side, were decrepit and poorly maintained, and represented the largest concentration of real estate in those areas under the control of a single group.