What is the main, or central, idea of the passage?

What is the main, or central, idea of the passage?
The Triangle Shirtwaist Factory fire killed almost 150 factory workers, who were trapped inside due to a locked exit and a broken fire escape.
Despite a strike by garment workers, the owners of the Triangle Shirtwaist Factory refused to support unionization.
Because of the Triangle Shirtwaist Factory fire, the government began to regulate working conditions in factories.