How did "boundaries of American freedom" grow narrower during the 1890s?
The 1890s are not typically seen as a time of great repression. However, if you want to argue that American freedom was limited during that time, you should focus on the rights of workers to form unions and fight for better wages and conditions.
There were major strikes during the 1890s that were crushed using violence as well as government action. Important examples include the Homestead Strike and the Pullman Strike. The Sherman Antitrust Act was used against unions, leading to things like a 6-month jail sentence for Eugene V. Debs. The crushing on the unions through violence and through laws can be seen as a curtailment of American freedoms.