What is David Von Drehle's thesis?

Von Drehle states his thesis in the Prologue. He claims that the Triangle Fire in 1911 was not only a terrible industrial disaster—it was "the crucial moment in a potent chain of events—a chain that ultimately forced fundamental reforms from the political machinery of New York, and after New York, the entire nation." The Triangle fire occurred in the midst of the Progressive era, when reform-minded politicians and activists sought to tame the abuses that accompanied industrialization and the rapid growth of cities. Reformers met with stiff opposition from business owners, laissez-faire minded politicians, and the corruption of urban political machines like Tammany Hall. These forces combined against striking garment workers (including Triangle employees) in the years preceding the fire, but the fire had the effect of building public sympathy for the workers and thus for reforms aimed at protecting them. While Triangle is primarily a narrative, not exactly an argument-driven monograph, this is the crux of what Von Drehle is trying to say. The Triangle catastrophe, in part because of who it affected (the fact that they were mostly young women was significant, but so was their previous notoriety as striking workers) was a catalyst for major change.
https://books.google.com/books?id=Xw4fjRQFusQC&printsec=frontcover&dq=triangle+fire+that+changed+america&hl=en&sa=X&ved=0ahUKEwigi_mExY_ZAhUpjK0KHXCtBcQQ6AEIKTAA